THE IDENTIFICATION OF LARVAE OF SOME SPECIES
OF BARK BEETLES BREEDING IN CONIFEROUS TREES
IN EASTERN CANADA
A THESIS
Submitted to the Faculty of Graduate
Studies and Research of
McGill University
By
J.B.Thomas
In Partial Fulfilment of the Requirements
for the Degree of
Doctor of Philosophy
October, 1954 TABLE OF CON'I»JTS
I. Introduction . . 1 II. Review of Literature ...... 3 III. Materials and Methods ...... 6 IV. Species of Bark Beetles Examined •••••••••••.•••••••••.•••• 9 V. Description of the External Anatomy of gylurgops pinifex
(Fitch) as Typical of Scolytid Structure •••••••••••••••••• 12 A. General ...... 12 B. Head ...... 13 C. Mouthparts ...... 17 1. Labrum and Epipharyngeal Lining ...... 17 2. Mandible ...... le 3. Maxilla ...... 19 4. I...a.bium •••.•••.•••.•••••••••••••••••.•••••.••••• 20 Hypopharynx ••••• ...... 21 D. Thorax and Abdomen .••..•.•.•.•...... •...••.••..... 21 Dorsum ...... 22 Pleuron ...... 31
3. SterntlID •••.••••••••.••••••••••••.•••••••••••••• 33 VI. Comparative Anatomy of Species Studied . . 36 A. General Discussion of Setal Nomenclature . . 36 B. Integument Including Setal Pattern . . 46 C. Head Capsule Including Setal Pattern ...... 53
D. Labrum ••••••••••.••••••••••••••••••••••••••••••••••• 61
E. Epipharyngeal Lining •••••••••••••••••••••••••.••.••• 62 F. Mandible ...... 64 G. Maxilla 65
H. Labf.um •••••••••••••••••••••••••••••••••••••••••••••• 66 VII. Identification of Genera and Some Species Examined ...... 70 Genus Conophthorus ...... 78 II Crypturgu.s •••...... •.•.•••••...... •••...•....•. 81
II Dendroctonus · . 84 II Dryocoetes •...... •...... 89 II Gnathotrichus ...... 92 II ByItt.rgops ••••..••••••..••••....•.•••.••..•••.•..• 95 II Orthotomicu6 · . 98 II Phloeosinus ...... 101 II Pityogenes ...... 103 II Pityokteines · . 106 II Polygraphus ...... 109 °11 Pityophthoru5 ...... 111 II Scolytus ...... 114 " TryPodendron .••...... •...... • 117 VIII. Observed and Recorded Hosts ...... 120 IX. Average Length of Larvae and Adults of Species Examined••• 123
x• SlJIIlIIla17 •••••••••••••••••••••••••••••••••••••••••••••••••• 125 XI. Bibliography ...... 127 Plates I to XIV I. INTRODUCTION
The use of the external anatomy of the larvae of bark beetles for the purpose of generic and specific identification has been neglected in the past. One reason for lack of interest in this particular phase of the study of bark beetles may lie in the biology of this group of insects where, in many cases, adults are present together with the larvae throughout most of the developmental period. However, there are occasions where larvae of more than one species feed in the same area of bark, and even though adults of all species represented are present, the percentage of each species cannot be estimated. This becomes important in population studies where, in order to obtain reasonably accurate results, all stages of each species must be counted. Also, there are occasions when the adults have emerged leaving only immature stages and here a key to the larvae is required. The small size of most bark beetle larvae of course necessitates the use of minute anatomical characters in separating one genus from another or species within a genus. This factor may lessen the usefulness of the keys for quantitative work since rapid examination of key characters is important. The use of minute and often obscure points of comparison should have no serious effect on the value of the key for qualitative purposes where the only need is to be able to say certain genera and species are repre sented in a particular community. An additional complication in the identity of bark beetle larvae occurs when weevil larvae, feeding in the same host, mingle with the bark beetle larvae. To date, there does not appear to be any positive means, other than rearing, of separating larvae of the families Scolytidae and Curculionidae. Identification of species of bark beetles has been made on the basis of imaginal characters, for which there are many out standing publications. There is also available in the literature, information on host specificity of many species as well as descriptions of the galleries and larval mines characteristic of certain genera. There has been to my knowledge no comprehensive study of the larvae of species of bark beetles occurring in eastern Canada for the purpose of separating them by anatomical characters. In the hope of establishing a satisfactory method of doing this and thereby adding a new working tool to those already available for identification of genera and species of Scolytidae, the results of my examination of the larvae of a number of spec~es of bark beetles are presented. While the number of species examined has not been as extensive as originally planned, it is my contention that the results of this study will begin to fill a gap in the published literature on bark beetles.
The geographic boundaries of the areas, fraa which species being studied were selected, are not as restrictive as would appear at first since few species of bark beetles common to eastern fauna are found in the fauna of 'Western Canada, particularly in western Alberta and British Columbia. The restriction of this study to species breeding in coniferous trees is a natural one since I know of no one species which breeds in both coniferous and hardwood trees.
When specimens or a sufficient number of species breeding in hardwood trees become available, it is hoped to make a separate study of the larval characteristics. - :3 -
It is a pleasure to acknowledge the assistance of a number
of collectors and institutions in providing material which I was
unable to collect myself. Mr.N.R.Brown, University of New Brunswick,
obtained a number of specimens of Dendroctonus simplex Lee. for me
from the Science Service Laboratory, Fredericton, N.B. A further
collection of this species was provided by Mr.A. T.Drooz of the Forest
Insect Laboratory, Milwaukee, Wisconsin. Mr.L.Lyons of the Forest
Insect Laboratory, Sault Ste.Marie, Ontario, gave me specimens of
Conophthorus coniperda (Sz.) and Q.. resinosae Hopk , , and the United
States National Museum, Smithsonian Institution, loaned specimens of Ips calligraphus (Gem.), I. borealis Sw., Pithophthorus consimilis Lee. and f. puberulus Lec. For valuable criticism offered in the preparation of the manuscript by Dr.E.M.DuPorte, Macdonald College, and members of the Forest Insect Laboratory, Sault Ste.Marie, Ontario,
I am very grateful. Photographic reproduction of the drawings were made by Mr.D.C.Anderson and Miss E.Heino. Dr.M.L.Prebble, Chief,
Division of Forest Biology, Science Service, Department of Agriculture,
Ottawa, kindly granted permission for the use of the departmental data
included in this thesis.
II. REVIn4 OF LITERATURE
There are many important and useful publications classifying
the species of Coleoptera on the basis of imaginal characters. Perhaps
the most noteworthy of these in North America are Blatchley's (1910)
Coleoptera of Indiana and Blatchley and Leng (1916) Rhynchophora or
Weevils of North Eastern America. Also, classifications to families of coleopterous larvae have been published by a number of authors with - 4 -
five very useful ones appearing in the English language. MacGillivray (1903) published a key to some of the more common families of coleopterous larvae, although determinations to many larvae were incorrect according to Peterson (1951). A more comprehensive and accurate key to most families of Coleoptera was published by Roberts (1930). Boving and Craighead's (1931) illustrated key to the principal larval forms of the order is an excellent article on this subject, particularly for advanced students. Keys to the families of larvae of beetles of the British fauna were published by VanEmden (1942). Finally, Peterson (1951) published the results of his study of larval Coleoptera, his revision of Robert's key resulting in a form more satisfactory than the original for North American species. While the keys are to families only, the book is profusely illustrated with diagrams of many species of each family featuring their diagnostic characteristics.
Classifications of species of Scolytidae have been based almost solely on imaginal characters, a number of the most important taxonomic papers being those of Swaine (1918), Blatchley and Leng (1916), Hopkins (1909 and 19l5a and 1915b), Chamberlin (1939), Dodge (1938) and
Beal and Massey (1945). To my knowledge, only one author has attempted a comprehensive classification of bark beetle larvae, Hopkins (1909), who included in his treatise on the genus Dendroctonus a division of the species of that genus based on larval characteristics. Earlier, in 1905, the same author stated that larval characters referred the species of Dendroctonus into practically the same position as had the adult characters and my even have indicated closer natural affinities. Other references to 8colytid larvae in the literature are concerned mainly - 5 ..
with descriptions of isolated species. Of this type, a few in particular are extremely useful for comparative studies of individual species. Russo (1926) published the biology and morphology of
Chaetoptelius vestitus Fuchs, introducing a system of nomenclature for the setal patterns on the head and bod;y. An account of the morphology of the genus Gnathotrichus Eich. was published b.Y Schedl (1931) but his discussion of the larvae was restricted to one species, Q. materiarius
Fitch. A detailed description of the larva of the native elm bark beetle, Hylurgopinus rUfipes (Eich.) was published by Kaston (1936).
In many of the published keys to the larvae of Coleoptera, the families Scolytidae and Curculionidae appear together as the authors either claim directly or infer that the larval forms of these two families are inseparable. This is the case in the publications of
Roberts (1930), BOving and Craighead (1931), Chu (1949) and Peterson
(1951). However, in particular instances, it appears that certain weevil and bark beetle larvae can be separated. Wallace and Beard
(1942) published a brief description of characters which could be used to separate larvae of two species of bark beetles, Scolytus multistriatus
(Marsh.) and Hylurgopinus rufipes from two species of weevils of the genus Magdalis. 'lhese three species often occur with galleries inter- laced in the same area under 'the bark of e1m trees. In a later section
I will report on characteristics which I have found useful in separating three species of Curculionidae from bark beetle larvae. /.
A review of the literature on coleopterous larvae shows that much more work has been done on the separation of genera and species of
Curculionidae than has been done on Scolytidae. Important contributions - 6 -
have been made by' Roberts (1926) Van Emden (1938) and Boving (1929).
Anderson (1947) published a paper detailing a terminology for the anatomical characters useful in the taxonomy of weevil larvae. This author has been engaged in a comprehensive study of the larvae of
Rhynchophora exclusive of Scolytidae and Platypodidae, and has published a number of papers on this subject (Anderson,1941, 1948&,
1948b and 1952).
III. MATERIALS AND METIDDS
Specimens of the larvae of thirty species of bark beetles, listed in section IV, were obtained. To ensure that the specimens of larvae were the progeny of adults which could be identified or had been identified, the following methods were employed:
(a) Larvae were removed from isolated galleries in which the
Parent beetles were still present.
(b) Larvae were removed from larval mines which could be
traced back to the main gallery and where part of the
same brood had developed to the adult stage.
(c) Larvae were obtained by rearing individual species.
(d) Some species were received from collectors who were certain
of the identification of the parents and also fran reference
collections of various laboratories and museums.
The larvae were preserved in 70 per cent alcohol and examin ation of whole specimens was made in watch glasses either in distilled - 7 - water or in glycerin. To study the comparative structure of different species, the complete head capsule, as well as individual parts of it, and mouth parts were mounted on glass slides using Hoyer's solution as a medi\Dll. Hoyer-!s solution was found to be more suitable in sane ways than Canada balsam as a mounting medium since specimens could be taken directly from either water or alcohol of any percentage and mounted.
The majority of the parts being mounted were minute and delicate result ing in considerable loss and damage when they had to be taken from a water stain through alcohols of increasing concentrations and into xylol for motmting in Canada balsam. The glycerin used in Hoyer's solution had a tendency to remove the colour from stained specimens although
Gage's acid fuchsin was more permanent than other stains tested. A second difficulty encountered when using Hoyerts solution was the inability to keep it under the cover slip when the thickness of the specimen being mounted necessitated supporting the cover slip on chips of glass. Most difticulty occurred when the cover slip was raised by more than twice its own thickness. Ordinary slides, 25 x 75 mm., were suitable for most material but, where large head capsules were mounted, it was found convenient to use hanging drop, microscope slides.
The larvae were decapitated and the mouth parts carefully removed from the head capsule. All parts were then placed in a 10 per cent solution ot KOH for several hours after which it was possible to remove the loosened muscle and connective tissue with fine forceps and dissecting pins, finally flushing the macerated tissue with water or alcohol using a syringe with a finely drawn-out glass tube. It was discovered that frequently these tedious cleaning steps could be avoided - s - if specimens which were moulting, pupating, or had just completed pupation, were available. With these, the head capsule had split into three sections along the ecdysial suture and could be removed from the pupa or the head of the next instar larva entirely free of muscle tissue.
Entire head capsules could be obtained if the specimens had not proceeded to the point of splitting of the head capsule. If pupation was canplete, the shriveiled-up last larval skin would frequent4r adhere to the posterior abdominal spines of the pupa and sections of the head capsule and the mouth parts could be separated from the larval skin.
Parts of the body were overstained in Gage's acid fuchsin, usually 20 to 30 minutes, and then immersed in a 10 per cent solution of
KOH for one or two seconds. This appeared to remove all the stain immediately, at which time the parts were washed in water or alcohol for a few minutes prior to mounting to remove the KOH which forms a white precipitate with Hoyer's solution. When finally placed in the mounting medium, a part of the stain re-appeared. This technique produced a better stained specimen than could be oi::tained by only a light, initial staining.
Some of the drawings were made with the use of a squared Whipple disc inserted in the eyepiece of a binocular microscope or compound microscope, depending upon the magnification required. However, many of the drawings were traced from images of mounted specimens projected through a compound microscope onto a frosted glass plate. The plate,
10 by 12 inches, was fixed to the end of a box 10 by 12 inches by 3 feet long constructed of quarter-inch plywood. This was placed horizontally' on a desk, the slide with the object to be drawn placed on the microscope - 9 -
stage and the microscope boqy rotated on its foot into a horizontal
position, where the image could be projected onto the frosted glass
plate by means of a strong beam of light shining directly through the
condenser and lens system of the microscope. '!he size of the image
could be increased or decreased by varying the distance between the
frosted glass plate and the microscope. When the image was sharply
focussed, a tracing was made directly onto engineering tracing paper.
Details missed in the copying were later filled in by examination of
the specimen through the microscope. Drawings obtained in this manner were not bilaterally symmetrical as the specimens were frequently
distorted in the mounting medium. However, it greatly facilitated the
accurate reproduction of different parts. The thickness of head
capsules and mandibles made it impossible to obtain a clear image, and
drawings of these were made directly from the microscope onto squared
paper.
IV. SPECIES OF BARK BEETLES EXAMINED
Swaine (1918), in his bulletin on Canadian bark beetles, lists
thirty-nine species representing eighteen genera which may occur in
coniferous trees in Canada fram the north-western part of Ontario east ward into the maritime provinces. An additional species, PitlOphthorus
pulchellus Eich., which Swaine lists as occurring in the eastem United
States, has been found by the writer in north-western Ontario. Larvae
of only thirty species representing fifteen genera have been examined
since it was found impossible to obtain specimens of all the species
required. That this group of insects has been neglected by collectors
of inunature stages was emphasized by the results obtained from requests - 10 - for larval material. Enquiries made at various entomological laboratories in eastern Canada, the Canadian National Collection at Ottawa, the Universities of New Brunswick, Manitoba, Michigan and Ohio, The New York State College of Forestry, Macdonald College, the Redpath Museum of McGill University, the Forest Insect Laboratory, Milwaukee, Wisconsin, the General Biological Supply House, Chicago, the Museum of Comparative Zoology at Cambridge, Mass., the State Natural History Survey Division, Illinois, and the United States National Museum, Smithsonian Institution, provided only four species which I had not already collected.
Three species were kindly provided by individual collectors.
Listed below are the names of the species examined as well as those species which were not available. The spelling of the names and the authorities are as in Leng's (1920) Catalogue of the Coleoptera of America and supplements 1 to 5 prepared by Leng and Mutchler (1927,1933), Blackwelder (l939) and Blackwelder and Blackwelder (1948).
Species Examined Subfamily Hylesininae
Crypturgus atomus Lee. Dendroctonus piceaperda Hopk. " rufipennis (Kby.) " simplex Lee. " valens Lee. Hylurgops pinifex (Fitch)
Phloeosinus canadensis Sw. Polygraphus rufipennis (Khy.) -11-
Subfamily Sco~tinae
Scolytus piceae Sw.
Subfamily Ipinae
Conophthorus coniperda (Sz.)
II resinosae Hopk. Dryacoetes affaber (Mann.)
II americanus Hopk, Gnathotrichus materiarius (Fitch) Ips borealis Sw.
II cailigraphus (Germ.)
II chagnon! Sw.
tt perturbatus (Eich.)
II pin! (Say) Orthotomicus caelatus (Eich.) Pityogenes hopkinsi Sw.
II plagiatus (Lec.) Pityokteines sparsus (Lec.) Pityophthoru8 consimilis Lec.
II nudus Sw.
tt puberulus Lec.
II pulchellus Eich.
II Spa Group VI (Referred to as species "a") " Spa Group VI (Referred to as species "b") Trypodendron tn."ittatum (Kby.) - 12 -
Species Not Available
Subfamily Hylesininae
Hylastes porculus Er.
Phthorophloeus piceae Sw.
Subfamily Ipinae
Cryphalu8 balsameus Hopk.
Ips laticollis Sw.
" longidens Sw. " perroti Sw. Myeloborus ramiperda Sw.
Pityophthorus cariniceps Lee.
" nitidus Sw.
opaculus Lee.
pulicariu8 (Zimm.)
Trypodendron rufitarsus (Kby.)
v". DESCRIPTION OF THE EXTERNAL ANA'IOMY OF !{ylurgops pinifex (Fitch) AS TYPICAL OF SCOLYTID STRUCTURE
A. GENERAL
The body is curved dorsally into a shallow crescent shape characteristic of most species of bark beetles. Mature larvae average
6.49 mm. in length based on measurements of eighteen specimens. The head is hypognathous in position, yellow-brown or amber in colour, the · mandibles and epistomal region a darker brown to black, the remainder of - 13 -
the boqy a creamw-white colour. Each of the thoracic and abdominal segments is composed of a .number of integumental folds, not separated by distinct sutures, which give the larva a generally wrinkled appear ance (figures 1, 2 and 3). The larva is apodous but each thoracic
segment bears on the ventral surface a pair of lobes having a definite
sclerotized area set with setae which may be used in locomotion. In addition to these lobes, almost the entire surface of the integument is
covered with fine,backward projecting,cuticular spines, which are probably of considerable assistance in anchoring the body in the larval mine and in forward movements. The head, thorax and abdomen bear a number of setae, the position of which will be discussed under their respective sections and in the descriptions of genera and species.
The head is hypognathous in position (fig.2) and normally is retracted toward the prothorax thereby concealing the narrow band of cervical membrane. The head capsule is slightly longer than wide, the
sides being sub-parallel continuing into a broadly rounded, caudal region. The cranium is divided by the ecdysial line which is Y-shaped.
The stem of the Y is the coronal suture (fig. 6) which appears double for a part of its length where it parallels the m1dcranial inflection. The frontal sutures, forming the arms of the Y, -proceed latero-ventrally to end at the membranous areas around the bases of the antennae (f1g8.5 and
6). The midcranial inflection is apparent internally as the midcranial apodeme (fig. 7) and externally as a suture extending part way into the frons (fig. 6). While there is not a distinct epistornal suture, the anterior edge of the frons is more darkly pigmented and is inflected - 14 -
internally to form the epistomal apodeme (fig. 16). The lateral angles
of the epistomal area, on either side of the clyPeus, are produced
anteriorly to form the dorsal, articulatory processes of the mandibles,
(figs. 5, 6 and 7).
The outer edge of the dorsal articulation of the mandible and
the inner border of the basal membrane of the antenna are in juxtaposition.
An indistinct suture is visible externally, proceeding posteriorly fran
this point into the frons, almost reaching the frontal suture (figs. 5
and 6). Internally, there is a corresponding apodeme continuous with
the epistanal apodeme and at right angles to it. From the position of
the internal ridges, I interpret the external line as representing the
frontogenal suture with the corresponding frontoaenal apodeme. Hopkins
(1909, fig.40E, page 59) has indicated the presence of this suture in
his drawing of the head of the larva of Dendroctonus valens, but has not named it. Schedl (1931) and Kaston (1936) do not describe such a suture
in their papers on the morphology of the larvae of the genus Gnathotrichus
and of Hrlurgopinus rufipes respectively.
The edge of the oral foramen proceeding from the antenna to
the ventral articulation of the mandible is thickened and inflected
to form a strengthening rim, the subgenal inflection, (fig. 5).
Continuing posteriorly, the rim of the oral foramen remains inflected
forming an internal ridge proceeding from the ventral articulation of the mandibles into the gena for a short distance (fig.5 and 7,Ha). This is
the hypostomal apodeme if one follows the system used by Snodgrass (1935)
in calling the sclerite cut off from the gena beyond the posterior, mandibular articulation, the hypostoma. Outwardly, this ridge is marked - 15 - by the hypostomal suture and a hypostomal lobe projects into the foramen at the point of articulation of the maxilla (fig.7,Hs).
The postocciput is a slightly inflected, narrow rim of the occipital foramen cut off by the postoccipital suture (fig. 7,Poc). Posteriorly, the postocciput is continuous with the midcranial apodeme. The neck membrane is attached along the line of the postoccipital suture. The tentorial bridge, apparently formed by the fusion of the posterior tentorial arms, forms a strong support between the sides of the head (figs. 5 and 7, t.b) and separates the oral and occipital foramina. There are two projections on the posterior edge of the bridge to which muscles are attached. The anterior tentorial arms arise internally from points at the anterior edge of the frontogenal sutures, proceed posteriorly for a short distance parallel to the inner surface of the frons and then are connected by slender ligaments to the anterior edge of the posterior tentorial bridge (figs. 5 and 7). The anterior tentorial pits are not visible. A ligamentous rod connects the opposing sides of the ventral edge of the oral foramen just posterior to the ventral, articulatory processes of the mandibles (figs 5 and 7). This is the hypopharyngeal bracon which supports the hypopharynx.
The number and arrangement of setae and sensilla on the head capsule is indicated in figures 6 and 7. In the following description, the figures quoted are for the setae and sensilla located on one-half of the head capsule only. Since the setae are seen to best advantage when the head capsule is mounted on a slide, the position of the setae has been given with the head capsule in a prognathous orientation which places the actual anterior surface in a dorsal position. The frons - 16 -
bears five setae, numbered 1 to 5, beginning posteriorly and proceed
ing anteriorly to number 5 located at the anterior end of the
frontogenal suture. Numbers 1 and 2 are alongside the endocarinal line wi th a single sensillum located about midway between the two. Number 4
is anterior and lateral to number 2 in the anterior half of the frons,
with number 3 lateral and posterior to it. A second sensillum is located close to seta number 4. One pair and a group of three setae located on the parietal region are called the dorsal epicranial setae
(fig. 6, Des). Number 1 is mesal to 2 about one-third of the distance along the vertex of the epicranium beyond the posterior limit of the
frons, with number 1 nearest the coronal suture. The group of three
setae is located lateral to the frons in a triangular formation. Dorsal epicranial seta 3 is close to the frontal suture, number 4 lateral to
number 3 and the fifth one anterolateral to number 4. Three sensilla are associated with the dorsal epicranial setae (fig. 6, Desl). Sensillum
1 is posterior to seta number 1 and number 2 is usually slightly
posterior to seta 1 but may lie very close and lateral to it between numbers 1 and 2 setae. The third sensillum is located approximately on a line between setae numbers 3 and 5. A row of four very minute setae, posterior epicranial setae (fig. 6, Pes), begins posterior to dorsal epicranial seta 2 and proceeds posteriorly, curving mesally. A single
sensillum is located outside of this row near posterior epicranial seta
2 (fig. 6, Pesl). A pair of setae located near the anterior region of the head capsule and lateral to t he anterior group of dorsal epicranial
setae, are referred to as lateral epicranial setae, number 1 being the most posterior (figs. 6 and 7,Les). Two sensilla are associated with
these, one between the two setae and one posterior to seta 1 (fig.7,Lesl). • - 17 ...
The final pair of setae are minute, located on the ventral side of the
head capsule posterior to the ventral articulation of the mandible,
(fig. 7, Ves). Ventral epicranial seta 1 is the most posterior of the
pair. A single sensillum is located posterior to number 1 seta
(fig.7,Vesl).
The clypeus is a broad sclerite hinged to the anterior edge
of the frons, figures 6 and 8, with angular sides and a broadly
emarginate anterior margin. A pair of setae is located on each side
of the clypeus just anterior to the frontoclypeal suture with a single
sensillum in close proximity to each pair of setae but slightly anterior
in position. The innermost of these two setae has been numbered 1, the
outer 2.
c. MOUTHPARTS
1. LABRUM AND EPIPHARYNGEAL LINING
The labrum is a broad sclerite, narrower than the clypeus, movable on the clypeus by the clypeo-labral suture (figs.5, 6, 7 and 8).
The anterior margin, the median part of which is produced slightly-,
folds under and is continuous with the membranous inner lining of the
labrum and clypeus (fig. 16). The posterior edge of the labrum is drawn
out into a point extending below the clypeus and is visible externally
as a more darkly pigmented area (fig. 8). Attached to the anterior, . inner surface of the labrum are two sclerotized rods, the tormae (figs.
8 and 16), the free sections of which extend posteriorly, gradually approaching each other until in some cases a weak line of fusion occurs
between the posterior ends. The limit of the tormae is posterior to - 18 -
the clypeo-labral suture. The labrum bears dorsally three pairs of
setae labelled Lms 1, 2 and :3 in f\\gure 8. A single sensillum occurs in the centre of the labrum and another sensillum is located just lateraa of each seta number 1.
There is no epipharynx in the sense that the term was first introduced into insect morphology, but rather there is a membranous epipharyngeal lining of the labrum and clypeus extending into the oesophagus. The membrane is supported by the tormae and bears three distinct groups of setae. A median pair of stiff setae is located on the anterior edge of the epipharyngeal lining and a second group of three setae is located antero-laterally of the base of each torma (fig.16,Ams,Als). Setae of both of these groups are ver,y stiff and well developed. Three pairs of short setae are located between the tormae (fig.16,Mes). Also, there are two pairs of 8en8illa, in clusters of three, on the epipharyngeal lining, one pair on either side of the most posterior pair of setae (fig. 16, Esl).
2. MANDIBLE
The mandible is short, stout and heavily sclerotized, the dorsal or outer aspect being slightly convex as opposed to the concave, ventral or inner aspect. The cutting edge is sharp and bears three distally placed incisoral teeth as well as a much smaller tooth located about midway between the third tooth and the base of the mandible (figs. 11 and 12). The outer, posterior angle of the base of the mandible
bears a large, rounded condyle which articulates with the ventral, articulatory process of the head capsule. The mandible articulates dorsally with the articulatory process of the head capsule situated - 19 - lateral to the base of the clypeus. The contraction of abductor and adductor muscles, acting in a plane at right angles to the axis of the mandibulary hinge, operates the mandible. The muscle tendons are shown in figures 11 and 12, the inner, adductor tendon being much larger than the abductor one. '!he mandible bears two small setae on the outer surface in a vertical alignment and three sensilla, two at the base of the mandible on the outer surface and one mesad of the setae toward the cutting edge (fig.12).
J. MAXIlLA
The maxillae are situated alongside the labium and are membranously united with it as seen in figure 9. The cardo is a distinct basal sclerite broadly hinged to the base of the stipital region and articulating with the maxillary condyle of the head capsule.
The body of the maxilla is canposed of the fused stipes, palpifer and lacinial lobe, none of which are delimited by sutures. The palpus is two-segmented with the basal segment set in a membranous area of the palpifer. The distal segment bears a number of apical papillae. The lacinial lobe bears a row of seven, long, stiff setae on the dorsal side and a group of five setae plus a single seta on the ventral side (figs.
9 and 10, DIes, VIes). The outer margin of the lacinial lobe adjacent to the palpus is more heavily sclerotized and may represent the vestiges of the galea, a theory held by Hopkins (1909) concerning a similar area in the larva of Dendroctonus valens.
A long seta is located near the base of the stipital area with a sensillum ventral to it, and two long setae are bome on the edge of - 20 - the basal membrane of the palpus with a sensillum between the two.
A minute seta, together with a sensillum, is located on the inner angle of the lacinial lobe. The first segment of the palpus bears a minute seta and two sensilla while the distal segment bears a single sensillum.
4. LABIUM
The labium consists of a broadly rounded, semi-membranous, basal segment, the postlabium (fig. 9), which is connected to the prothoracic sternum b,y a neck membrane and laterally is connected membranously to the maxillae. The postlabium as described here corresponds to the submentum in Q. materiarius, li. rufipes and g. valens described b,y Schedl (1931), Kaston (1936) and Hopkins (1909) respectively. Similarly, the prelabium described below corresponds to the mentum of the same three authors. The postlabium bears three pairs of setae numbered consecutivelr from the posterior end to the anterior end (fig. 9,Plbs). The three setae are arranged in the form of a triangle with number 2 closer to number 3 than to number 1. The distance between setae number 1. is 1.ess than that separating the setae of the other two pairs.
The prelabium consists of a strongly sclerotized, trident shaped, premental sclerite, palpigers, pa1pi and a median, ligular.area.
The prementum has a distinct, posteriorly projecting, median section and three anterior projections, one median and two lateral ones. The anterior, median projection bears at its end a pair of sensilla and an additional pair of sensilla are located on the sides of the prementum - 21 -
just below the bases of the lateral projections. The lateral
projections extend into the palpigeral areas which support two-segmented
palpi. The segments of each palpus are approximately equal in length,
the distal one narrower than the basal one, and bearing a number of
apical papillae and one sensillum on the ventral side. The basal
segment also bears a sensillum on the ventral surface. The ligula
forms the median, semi-membranous lobe between the palpi and bears
two pairs of setae and a pair of sensilla. The two pairs of setae are
short and are located anterior to the median projection of the prementum.
One sensillum is located on either side of the two anterior pairs of
setae. A pair of long, prelabial setae are located, one each, in the
"U" shaped area between the median and lateral projections.
5. HYPOPHARYNX
The hypopharynx is a fleshy lobe forming the floor of the
mouth cavity, continuing into the oesophagus (fig. 15). The distal
portion, formed of a leathery, membranous tissue, has a concave, outer
surface and appears as an inner reflection of the ligula of the labium.
The lateral areas bear many cuticular spines while the proximal portion
is a sclerotized sheath partially encircling the oesophagus. The
hypopharynx is supported by the hypopharyngeal bracon ShOlCl in figures
5 and 7.
D. THORAX AND ABDOMEN
The body of the scolytid larva is divided into three thoracic
and ten abdominal segments with the tenth abdominal segment represented
indistinctly by anal folds (figs. 1, 2, J and 4). The segments are .. 22 -
delimited by intersegmental lines or grooves rather than by membranous
conjunctivae separating definite, sclerotized segments.
1. DORSUM
The dorsal area of the prothoracic segment is unmarked by
lines or grooves but the mesothoracic and metathoracic segments are
each composed of a small, median fold, elliptical in shape, followed by a transverse fold extending the full width of the segment (fig. 1).
The dorsal surfaces of the first eight abdominal segments are divided
into three folds but the delimitation of the folds on segment eight is very indistinct and can only be seen under- optimum lighting conditions.
The dorsum of the ninth abdominal segment is Wldivided. Immediately
above the dorsopleural groove on segments one to eight of the abdomen and on the metathorax there is a fold indistinctly delimited by a groove
proceeding anteriorly, ventral to the spiracle. These are referred to as laterotergal folds. The grooves marking these folds are missing on
the first two thoracic segments, however, the areas can be identified by
the presence of corresponding setae.
There is a tendency, evident from the literature, to apply the names of sclerites, which have been developed in specific cases to meet
specific needs, to other non-homologous areas of the insect boqy. To cite a few examples, Hopkins (1909) uses the terms prescutum, scutum,
scutellum and postscutellum to indicate integumental folds found in the dorsum of the larva of Dendroctonus valens which were developed in
response to the pull of segmental muscles. Boving (1914) adopted
Hopkins' terminology in so far a 8 it applied to campodeiform larvae and - 23 -
later used it in descriptions of the larvae of beetles of the subfamily
Galerucinae and the family Cleridae (Bovdng, 1929b, Bovfng and
Champlain, 1920, respectively). Craighead (1915, 1916 and 1924) continued the use of this terminology in describing ceramqycid larvae.
Roberts (1926) has designated areas of the dorsum in the abdomen of
some weevil larvae as prescutum, scutum, and scutellum. Sched-l (1931) and Kaston (1936) have followed a similar course in their work with scolytid larvae.
Much of the confusion in terminology arose fran early attempts
by workers to prove that each segment of the thorax was composed of four distinct rings or subsegments. The number of segments believed to have formed the thorax ranged from two to twelve, these theories being
advanced qy MacLeay (1830), Newport (1839), Hagen (1889) and Patten
(1890), both cited qy Martin (1916), Lowe (1890), Comstock and Kochi
(1902), Crampton (1909), Snodgrass (1909a) and others. Audouin (cited in MacLeay, 1830) recognized three segments and his interpretation then is essentially the one accepted today. The sclerites which he named prescutum, scutum, scutellum and postscutellum, he regarded as sub divisions of a single segment.
MacLeay (1830) referred to the thoracic segments as being the
second, third and fourth body segments, the head being considered a
single segment. Newport (1839) also based his studies on the work of
Audouin and called the prothorax, mesothorax and metathorax the second, third and fourth body segments, each being composed of four subsegments or annuli represented in the dorsum by the prescutum, scutum, scutellum and postscutellum. These he believed were partially fused in the pleural - 24 - region and completely so in the sternal region. Crampton (1909) and Martin (1916) criticized both MacLeay and Newport for their theory but it is possible that their interpretation of this work is in error. MacLeay and Newport each designated clearly a definite prothorax, mesothorax and metathorax and may have been using the term "subsegment" much in the way "sclerite" is used today to denote only a sclerotized area of the dorsum. As an example, atter describing the four pieces of the mesothorax as praescutum, scutum, scutellum and postscutellum, MacLeay stated "The above four pieces when united form the tergum of the mesothorax". To support the view that the terms prescutum, scutum, scutellum and postscutellum are incorrect when applied to larvae, it may be as well to review briatly the development of the thoracic tergum. Again there is confusion because of the different terminology used for various areas of a segment. Snodgrass (1931, 1935) considers the dorsal region of a segment as the dorsum, the ventral region as the venter and the lateral region lying between the dorsum and the venter as the pleural area. A major sclerotized plate of the dorsum is the tergum, the corresponding plate of the venter is the sternum and a single plate or group of plates in the pleural region is the pleuron. Component elements of these major areas are tergites, sternites, and pleurites respectively. This nomenclature has not been used by all research workers, for instance, Crampton (1914) applies the terms, dorsum and venter to the entire upper and lower surfaces of the insect body respectively. The entire dorsal region of each segment is the tergum, the ventral region is the sternum while the component sclerotized plates of these regions are referred to as tergites and sternites respectively. The entire lateral region of the - 25 - body is called the latus, while the lateral region of a distinct
segment is the pleuron. The terminology advocated by Snodgrass will be used in this paper.
There is a system of primary segmentation in the bodies of many arthropods including many holometabolous larvae where the
segments are separated by circular constrictions forming internal
folds to which are attached the longitudinal muscles. When sclerotization of parts of segments took place, usually the internal fold bearing the muscle attachment, a small anterior sclerite and a more extensive region posterior to the antecostal suture, became sclerotized leaving the posterior portion of the dorsum membranous.
The internal ridge is the antecosta, generally marked outwardly by the antecostal suture, and the sclerotized transverse area preceding the antecostal suture, which morphologically is a part of the preceding
segement, is the acrotergite. The definitive intersegmental conjunctiva is now the membranous area behind the large tergal plate, resulting in a condition of secondary segmentation.
In the thorax~ the generalized structure typical of secondary segmentation is retained in the apterygota, and in nymphal and many larval pterygota. The prothoracic tergum and sternum always lack ante
costal and precostal elements which apparently have been lost by membranization in the neck or posterior regions of the head. The external surface of the prothoracic tergum may be marked with sutures having corresponding ridges on the inner side. Crampton (1918) and
DuPorte (1919) have shown that these sulci, in the pronotum of
Dissosteira carolina and Rhomalea microptera respectively, are - 26 ... integumental folds formed b.Y mechanical stress and do not represent the prescutum, scutum, scutellum and postscutellum as was formerly assumed.
It is in the mesothorax and metathorax that specific modifications have taken place to accommodate these areas to the development of and action of the wings. The structural modifications have been outlined qy Snodgrass (1927 and 1935). The increased development of the longitudinal muscles of the wing-bearing segments necessitated the development of plate-like apodemes from the antecostae of the mesotergum, metatergum and first abdominal tergum which are known as the first, second and third phragmata. Since the wing movements are brought about by the curvature of the terga in the pterothorax, the terga of the two segments had to be modified, by elimination of the intersegmental membrane, to respond as a unit to the pull of the flight muscles. In the majority of winged insects, this has been effected in the following manner. The acrotergite of the mesotergum retains its usual form of a narrow flange whereas the acrotergite of the metatergum and the first abdominal segment are enlarged and extend forward to the posterior margin of the tergum preceding. The expanded acrotergites become the postnotal plates of the mesothorax and metathorax. In many of the higher insects, the phragmata may become separated from the original tergum b.Y secondarily developed lines of membranization and become more closely associated with either the preceding or following segmental plate. It is possible, therefore, for the segment bearing the major flight wings to have both anterior and posterior phragmata. The postnotum, as designated .. 27 .. by Snodgrass, is equivalent to part of the postscutellum suggested by Audouin (Snodgrass, 1909b), and this term has been used by Crampton (1914) and Martin (1916). The same sclerite has also been referred to as the pseudonotum by Snodgrass (1907).
To meet the strains imposed upon them by the wings, the terga of the wing-bearing segments have been strengthened by the development of various ridges on the inner surfaces through inflections of the integument. It is these sutures which divide the terga into the sclerites taken by earlier workers to represent various combinations of subsegments. According to Snodgrass (1935), these sclerites have no morphological counterparts in the terga of other segments. A prescutal suture with a corresponding internal ridge cuts off a narrow sclerite, the prescutum, immediately behind the antecostal suture. This Bclerite may be variable in shape and may be difficult to distinguish from the sclerite behind in cases where the prescutal suture is weakly defined or absent. The scut.um, lying behind the prescutum, is usually the largest sclerite and bears on its margins the anterior and posterior notal wing processes. It is separated from the scutellum by the scutoscutellar suture which is in the general form of an inverted "V" with the apex directed anteriorly. The scutellum may send a median tongue or shallow groove forward, dividing the scutum into two halves. Laterally, the posterior margins of the scutellum are prolonged into the axillary cords of the wings. The foregoing basic plan of the dorsum of a wing-bearing segment is, of course, subject to numerous modifications by movement of existing sutures and development of others. - 28 -
In Boft-bodied holometabolous larvae, the abdominal segmentation is for the most part primar,y in the sense that the longitudinal muscles remain attached to the original intersegmental lines, although there is a tendency for some of these muscles to became attached to other points of the integument (Snodgrass, 1935).
According to Snodgrass, a typical abdominal tergum has the sclerotiz ation in the form characteristic of a secondary segmental plate.
Anteriorly there is a marginal or sub-marginal ridge, the antecosta, to which the principal, longitudinal muscles have their attachments.
Generally, the antecostal suture is faintly marked and the acrotergite may var,y fran a scarcely perceptible rim to a wide flange. In certain cases the antecosta and the acrotergite are lost, the muscles becoming a ttached to the anterior edge of the ter-gum, Snodgrass goes on to state that in many insects, particularly larval forms, the dorsal sclerotizatiDn of the abdomen may be broken up into groups of segmental tergites.
These tergites are identified by position as mediotergites or latero tergites, or the mediotergites may again be subdivided. It would seem that in the larvae of same insects, particularly in Scolytidae, sclerotiz ation is almost entirely absent and therefore, the usual tergites are not defined. A similar situation is evident with respect to the pleural and sternal areas with the result that both the thorax and abdomen are devoid of sclerotized plates typical of many larval forms.
From the foregoing review of the specialized development of sclerites defined as prescutum, scutum, scutellum and postscutellum, it would appear clear that these terms should not be applied to folds in the integument of soft-bodied larvae where such folds are in response - 29 -
to the pull of segmental muscles and are not related to the develop
ment or function of wings. Parkin (1933), studying the larvae of
Anobiid beetles, recognized that the folds of the body wall could
not be homologized with divisions of the segmental sclerites of adult
insects, and accordingly devised a special nomenclature. Using his
system, a complete thoracic segment consisted of seven folds, a
prenatal, postnotal, two hypopleurals, two pedals and a sternal.
Anderson (1947) also departed from the use of terms restricted to
adult structure in describing the folds of the body of weevil larvae
although he still retained the sternellum in referring to a fold of
the venter of the abdominal segments.
In the scolytid larvae studied, the dorsum of the prothorax
is undivided and can be referred to simply as the prodorsum. The
dorsum of the mesothorax and metathorax is divided transversely by' a
groove into two folds to which I have allotted the numerals I, II,
for the anterior and posterior folds respectively. Three transverse
folds, to which I have allotted the numerals I, II and III, in order
from anterior to posterior, comprise the dorsum of each of the first
eight abdominal segments. The dorsum of the ninth abdaninal segment
is undivided, requiring no further designation, and the tenth segment
is represented by the anal folds. Using this simplified system, there
is no tendency to become confused with the specialized terms prescutum, scutum, scutellum and postscutellum, which are restricted to the thoracic sclerites of adult insects. The numbering sequence also
indicates the relative positions of the different folds. - 30 -
In discussing the setae present on the body of the larva, only those on one side of the segments, or one-half of the total number of setae, will be listed. The prothoracic dorsum consists of one fold only, having an irregular-shaped, sclerotized area, amber coloured, on either side of the midline. Each sclerotic area . bears five setae, with six additional setae located anteriorly and laterally to this sclerite and dorsal to the prothoracic spiracle, making a total of eleven setae for each side of the prothoracic dorsum. The typical arrangement of the setae is given in figures 1 and 2. The four most lateral setae are smaller than the remainder and are arranged in a line above the spiracle. The dorsum of the second and third thoracic segments is divided into an anterior and posterior fold, designated I and II respectively. The setal pattern for both segments is the same with fold I having a single seta near the midline and fold II with five setae in a transverse row beginning at the midline (figs. 1 and 2). Seta No.1, nearest the midline, is slightly separated from numbers 2, 3 and 4, while the fifth s eta of the row is separated from the remainder by an indistinct crease in the integument. In addition to these setae, a pair of setae is located below setae number 5 in both segments (fig. 1). These are referred t a as alar setae and are situated on small islands created in the integument by the absence of integumental spicules. They are separated from seta number 5 by an oblique crease in the side of fold II.
The dorsum of each of abdominal segments one to eight is divided into three transverse folds designated I, II and III proceeding posteriorly (figs. 1 and 2). The folds of segment number eight are - 31 - not as distinct as those of the preceding segments. A typical arrangement of the setae is shown in figures 1 and 2. Fold I has a single seta near the midline, fold II has no setae and fold III has five setae arranged in a transverse row and numbered from the midline laterally. Number 1 is separated from the remainder by a distance greater than that separating any two of the others. Setae 1, 3 and 5 are longer than numbere 2 and 4. A pair of setae is located dorsal to the spiracle and these are called spiracular setae. The anterior one is more dorsal than the posterior one and is usually the smaller of the pair. The dorsum of the ninth segment is not divided into folds and bears six setae in an irregular transveree row. The arrangement is not always conetant although the number six was fairly constant, consisting of three long setae and three short ones less than half the length of the longer ones, (figs. 1 and 4).
The tenth segment, represented by the anal folds bears a pair of minute setae on the fold lateral to the anal opening (fig.4). These are not always evident as they may become slightly infolded around the anus.
2. PLEURON
Hopkins (1909) describes an irregular groove or suture dividing the pleuron of each segment of the larva of Dendroctonus valens into an upper lobe, the epipleurum, and a ventral lobe, the hypopleurum, which, in the thorax, are said to represent the epimerum and episternum respectively. Schedl (1931) in the study of the morphology of the larva of Gnathotrichus materiarius adopts Hopkins' terminology but restricts the pleuron to an area above the longitudinal - 32 - fold or pleural fold of Hopkins. This area is again divided by another longitudinal groove into a dorsal part, bearing the spiracles in segments one to eight, which he called the epipleurite and a ventral part, the hypopleurite, but Hopkins called this latter lobe the epipleurite. The lobe ventral to the pleural fold which Hopkins called the hypopleurite, Schedl refers to as the sternellar area. The terminology given by Hopkins was also adopted by Kaston (1936) in his study" of Hylurgopinus rufipes but he considers that the groove referred to as the pleural groove or suture is undoubtedly the dorsopleural fold as outlined by Snodgrass (1931, 1935). The lobe above the fold is called the laterotergal and that ventral to the fold, the 1atero sternal, by analogy, although Snodgrass (1931) called it the pl.euron,
In this study of scolytid larvae, I have designated the folds lying between the dorsopleura1 and p1euroventral grooves as the pleuron. In abdominal segments one to eight there is a distinct groove or infolding separating a dorsal and ventral lobe which together comprise · the pleuron, figure 2. This groove is not as distinct in the thoracic segments or in the ninth abdominal segment. A dorsopleural line passing just ventral to the spiracles in segments one to eight of the abdomen separates the dorsum of the insect fram the dorsopleural lobe and a second line, the pleuroventral, separates the ventropleura1 lobe from the sternum. These lines are not as distinct in the thoracic and ninth abdominal segments but the position of the areas involved can be determined fram corresponding setae. The above interpretation of the pleural region appears to be in accordance with the position of the muscles of the body wall. Tergopleura1 and sternopleural oblique - 33 - muscles are inserted on the pleural groove. Also, there are intra-pleural muscles stretching from the dorsopleural and pleuro ventral lines to the pleural groove.
The folds making up the thoracic pleuron are indistinct compared to those of the abdaninal segments. A pair of setae lateral to the pedal area of the prothorax and borne on a small island of integument clear of spicules indicates the position of the ventro pleural lobe of the pleuron with the dorsopleural lobe absent. The presence of both dorsopleural and ventropleural lobes is indicated in the mesothorax and metathorax by the presence of a single seta on each lobe (fig. 2). The dorsal and ventral lobes of the pleuron of abdominal segments one to eight are distinctly delimited by integumental creases and each fold bears a pair of setae on small islands of smooth integument (fig.2, Dpls, Vpls). The pleural region of the ninth abdominal segment consists of a single fold bearing a single pair of setae, and the pleural region of the tenth segment cannot be distinguished as such.
3. STERNUM
The sternal area of each thoracic segment and segments one to seven of the abdomen is divided into four areas by shallow grooves. Anteriorly, there is a median area or mediosternal fold which is roughly triangular in shape on the prothorax and more broadly "u" shaped on succeeding segments. The posterior limit of this fold juts into a narrow transverse fold at the posterior end of the prothoracic and meso thoracic segments but only meets the corresponding fold on each of the - 34 -
succeeding segments up to the seventh abdominal. This transverse
fold is missing fran the eighth abdominal sternum. and the sternum
of the ninth segment is undivided. On each segment up to and
including the eighth abdominal, there is a laterosternal fold on
either side of the median fold. A small sclerotized circular area
bearing four setae is located on each lateral lobe of the three
thoracic segments. These are referred to as foot calli by various
authors.
As in the case of the dorsum, there have been terms used
to describe the folds in the sternum which are more appropriately
restricted to the anatomy of adult insects or at least to larvae
which have a sclerotized thorax and abdomen. Audouin (cited in
MacLeay, 1830) considered the lateral and ventral areas of the thoracic
segments as the pectus. According to MacLeay, if the sternum of each
thoracic segment was at its maximum of development, it, like the
tergum, would consist of four pieces and these he named praesternum,
sternum, sternellum and pos temua, Newport (1839) adopted MacLeay's
terminology although he could not find a fourth subdivision. Crampton
.<, iJ..9(9 ) would not use the tenninology given by MacLeay since it inferred " , : ..' -t- a relationship with the tergum, that is, that each segment originally
was composed of four armuli, and substituted the terms presternum,
basisternum, furcisternum, postfurcal sclerite and spinasternum.
Boving (1929a) has divided the sternum into eusternal and sternellar
areas. Roberts (1926) calls the anterior and posterior areas of the
sternum of the thoracic and first eight abdominal segments of some
weevil larvae, sternal and sternellar folds respectively. Anderson - 35 -
(1947) also divides the sternum. of weevil larvae into an anterior eusternal and posterior sternellar fold. Hopkins (1909) in his description of the larva of Dendroctonus valens designates the divisions of the sternum as sternal, sternellar and posternellar.
Schedl (1931) and Kaston (1936), both working with bark beetle larvae, used a similar division of the ventral folds of both thorax and abdomen.
In soft-bodied scolytid larvae, there are no individual sclerites Which can be designated as true sternites such as occur in some holometabolous larvae. Therefore, I do not think we are justified in giving to the integumental folds, which occur as a result of muscular tension, names such as presternum, sternellum and posternellum. DuPorte (1950)in a discussion of the thoracic sternum theorizes its development as follows: The definitive sternum is regarded as a composite structure formed ~ the union of two coxosternites with ventra sternites lying between the subcoxae, The latter may consist of a narrow transverse plate, the presternite, at the anterior of the segment, a larger mediosternite lying between the subcoxae, and a small inter segmental plate, the spinasternite, bearing an internal process, the spina. This latter sclerite is found only petween the first and second and second and third segments. The composite plate formed by the union of the two coxosternites with the mediosternite is the eusternum. The sternal apophyseal pits lie in the laterosternal sulci and a strengthen ing ridge, the sternacosta, develops internally between the apophyses, being marked externally qy the sternacostal sulcus which divides the mediosternite into an anterior and a posterior section. This sulcus .. 36 .. frequently continues across the coxosternites dividing them into anterior and posterior parts also. Since the laterosternal sulci usually disappear, the definitive sternum then consists of an anterior plate, the basisternite, and a posterior plate, the furcasternite. When the spinasternite unites with the furcasternite anterior to it, the resulting sclerite is the sternellum. It can be seen, therefore, that the sternum appears to have developed from existing sclerites and accordingly, the integumental folds in the ventral region of soft bodied larvae should not be construed as representing specific sclerites.
The number and location of the setae on the sternum is indicated in figures 2 and 3, and similarly to the description of the dorsum, the number of setae given represents those present on one- half of the body only. There is a single seta present on one side of the midline of the mediosternal fold in each thoracic segment and a pair of setae in the corresponding location on abdominal segments one to eight. Each thoracic segment has a slightly sclerotized pedal lobe bearing four setae and mesad of this a row of three setae on the latero sternal fold. The laterosternal fold of each abdominal segment one to eight has a single seta. The sternum of the ninth segment is a single fold and bears a pair of setae on either side of the midline.
VI. COMPARATIVE ANATOMY OF SPECIES STUDIED
A. GENERAL DISCUSSION OF SETAL NOMENCLATURE
Russo (1926) developed a system of nomenclature for the setae on the head and body of one species of bark beetle, Chaetoptelius vestitus Fuchs, which was adopted and modified by Schedl (1931), for - 37 -
use in describing the setal pattern of Q. materiarius. Russo gave
individual names to most of the setae located on the head and mouth
parts but named groups of setae on the thorax and abdomen. Schedl's
modification appears to be in a reduction of the number of names by
giving a name to a distinctive group of setae and nwnbering the setae
within the group, at the same time, changing the Italian names to the
Latin form. The name used is descriptive as to position on the head or
body, that is, seta fronto-lateralis, indicates one of a group of setae
on the lateral region of the frons. A comparison of the two systems as
given by Schedl is illustrated in Tables I and II at the end of this
section. Kaston (1936) adopted Schedl's new nomenclature in his work
on the morphology of !i. rufipes. modifying it, where necessary, to
conform to differently interpreted morphology. On the other hand,
Hopkins (1909) discounts the value of the setae in the descriptive
anatomy of Q. valens. stating that "With the exception of the scatter
ing hairs on the head and on the scutellar lobes of the thoracic and
abdominal segments, the body is without distinguishing vestiture.".
The foregoing have been, as far as I am aware, the only systems used for
describing the setae found on the head and body of scolytid larvae.
Anderson (1947), working with the closely allied larvae of
Curculionidae,has developed a nomenclature for the setal pattern of
the head and body. 'lbe setae on the head are numbered and referred
to as frontal, epicranial or clypeal depending on their location. The
epicranial setae are further subdivided as to position, that is, dorsal,
ventral, lateral or posterior. The setae on the thorax and abdomen are numbered and identified by reference to the particular lobe or fold of - 38 - the segment on 'Nhich they are located. Setae on the mouth parts have been identified by calling them labral, epipharyngeal, mandibular, maxillary or labial, and numbering them.
Anderson's system of nomenclature embodies in it several features which have influenced me in using it rather than that outlined by Russo or Schedl as a basis for describing the setae of scolytid larvae. The terminology is in English and terms such as prescutum, scutum, etc, the use of 'Nhich has been discussed in a previous section, have been omitted for the most part. The names applied to various setae or sensilla, or to groups of these, indicate to a certain degree the general location of each on the body. In the case of certain groups of setae, the relative position of setae within the group is indicated by the use of numbers after the name applied to the group and, of course, is contingent upon having the direction in which the numbering proceeds . clarified. For groups of setae in which no orientation of individual setae is evident, only the total number comprising the group can be given. An additional factor in favour of using Anderson's system, or one very close to it, is the evident similarity in the anatomy and setal patterns of larvae of Curculionidae and Scolytidae. For identification purposes, it is better to employ a nomenclature which permits a ready comparison of the setal patterns ot the larvae of the two families.
Giving the same number to a seta in a corresponding position may infer an homology where none is proven, but for comparative purposes only, the numbering system is quite satisfactory. In this study of scolytid larvae, I have adopted the use of both names and numerals but am not necessarily claiming homologies, which have not - .39 - been studied, for similarly numbered setae in different species or on different parts of the body of anyone species. Names of setae and sensilla found on the head capsule, mouth parts, thorax and abdomen of scolytid larvae are listed below together with the abbrevi ations used on illustrative figures at the end of the paper. Modifications of the terminology used by Anderson for weevil larvae have been made where necessitated by differences in structure or to conform to my interpretation of the larval anatomy of Scolytidae.
Used on the Head Capsule: Pes Posterior epicranial setae Figure 6 Des Dorsal II II " Les Lateral II " Figures 6, 7 Ves Ventral II II Figure 7 Fs Frontal setae Figure 6
Desl Dorsal epicranial sensilla II
Leal Lateral II II Figure 7 Vesl Ventral " " II Fsl Frontal sensilla Figure 6 Peal Posterior epicranial sensilla "
Used on the Labrum and Epipharyngeal Lining:
Lms Labral setae Figure 8 Ame Antero-median setae of epipharyngeal lining Figure 16
Als Antero-lateral II It II II II
Mes Median epipharyngeal setae II
Esl Epipharyngeal sensilla II
Lmsl Labral sensilla Figure 8 - 40 -
Used on the Clypeus: Clps Clypeal setae Figure 8
Clpsl II sensilla "
Used on the Mandible: Mds Mandibular setae Figure 12
II Mdsl II sensilla
Used on the Maxilla: Sts Stipital seta Figure 9 DLcs Dorsal lacinial setae « 10
VLcs Ventral II II Figure 9
Mxps Seta on maxillary palpus II Pls Palpiferal setae n
Stsl Stipital sensilla II
PIsl Palpiferal II II
Mxpsl Sensilla on maxillar,y palpus II VLcsl Ventral lacinial sensillum
Used on the Labium: Plbs Postlabial setae Figure 9
Prbs Prelabial setae II
Lis Ligular tI II Usl " sensilla " Pmtsl Premental tI II
Used on the Thorax and Abdomen: lTs Prothoracic dorsal setae Figure 1, 2
2TIs Mesothoracic dorsal setae, fold I II w 41 - zrrre Mesothoracic dorsal setae, fold II Figure 1, 2
3Tls Metathoracic .. .. "I II
3Tlla " "" "II II Ala Abdominal setae, fold I, segments 1-8 II
II AllIs "" "III, " II
9As Dorsal setae, 9th abdominal segment II 2, 4 lOAs Anal setae " 3, 4
DPls· Setae of dorsopleural lobe II 2 VPla " "ventropleural lobe " Ps Pleural setae " Sps Setae of spiracular area II As Setae of alar area, mesothorax and metathorax " Msts Mediosternal setae " 2, 3 Lata Laterosternal setae " Sts Sternal setae of 9th segment " Peds Pedal setae, thoracic segments " TableI. Setae of the head as described by Russo (1926) and Sched! (1231)
< Russo Used on Schedl Used on Setole mediane-distale Frons Seta fronto-lateralis Frons II submediane II II " II II II latera.li II " If If If
II basali Frons-epistoma If epistomalis Epistoma
II II clypeali Clypeus II clypei Clypeus
" mediane distali LabrtDll If labralis Labrum If premediane II If II f:; " I II sublaterali II II II II II basali-laterali " II II II II verto-mediana Vertex
II verto-lateralis II
.. laterale del vertice Genae II geno-lateralis Genae
II mediane u II II II II II basale II II II " " II interna del vertice H II II II II Setole della gena Genae Seta geno-mediana Genae " mediane It " " " \I esterna " \I " II " basali " " \I \I \I epicrano-lateralis Epicranium " dorsali Mandible \I mandibulae dorsalis Mandible It sublaterale-basale \I II II lateralis It
II \I maxillaris Stipes laterale delle stipite Stipes stipi tae I \I mediane del palpifero Palfifer II palpiferae maxillaris Palpifer e \I laterale del palpifero " \I It " " " palpiale First joint of palpus " palpo maxillaris 10 First joint of palpus It distale Submentum " submento-lateralis Submentum " mediane " \I " " II " subbasali " " " " " " menti Mentum " subbasali Mentum " labio palpiferis Palpiter of Labium Seto1e distale Ligula Seta 1egulae dista1is Ligula " mediane " II II mediana Jl II " " basalis "
Table II. Setae of the thorax and abdomen as described by Russo (1926) and Sched1 (1931) Russo Used on segments Sched1 Used on segments
Seto1e tergali mediana I, II, III, 1 ) Seta praescuti I, II, III, 1-9 ) , " proterga1i 1-8 ) t _ posttergali I, II, III,1-8 ) I " ) II tergali-laterali 1 ) Seta scutuli I) II, III, 1-9 ) " tergali 9 epip1euri I, 1-8 ) " ) 1 p1euri-stema1i 9 ) Seta epip1euricum I, II, III, 1-9 " ) u tergali-p1eurali II, III ) ipop1eurali I, 1-8 ) " ) 2 p1eurali-sternali 9 ) Seta hypop1euricum I, II, III, 1-9 " ) " epip1euri II, III ) Setole sternali-anteriori-externe I ) ) II -posteriori- II I ) " ) -mediane I ) " " ) II ipopleurale II, III ) Seta sternellaris I, II, III, 1-9 ) sterna1i-latera1i II, III ) " ) II -mediane II, III ) " ) II sternali 1-8 )
L ~ Not investigated Seta sternalis I, II, III, 1-9 VI
Setole anali 10 Seta anails 10
1 The two dorsal setae 2 The two ventral setae - 46 -
B. INTEGUMENT INCLUDING SETAL FATTERN
The integument of the scolytid larvae studied, with the exception of three species of the genus Dendroctonus, offers few features useful in separating genera or species wi thin genera. The number and location of the integumental folds are exemplified qy
Hylurgops pinifex (figs.l, 2 and .3). '!he paired pronotal plates, which are amber-coloured and quite distinct in !!. pinifex and in certain other genera such as Dendroctonus, !J2[, Dryocoetes and Polygraphus, are only lightly pigmented and consequently are indistinct in other genera such as Orthotomicus, Scolytus, Conophthorus, Pityophthorus, Pityogenes,
Trypodendron, Gnathotrichus. and practically non-pigmented in the genera Phloeosinus, Pityokteines and Crypturgus. However, in those genera in which the pigmentation is slight or lacking, the pronotal plates become apparent after the integument is stained as they take on and retain a deeper colour than the surrounding tissue. Similarly, the small sclerotized plate on the prothoracic sternum varies from deeply pigmented and clearly visible in the genera !J2!, Dryocoetes, Pol:ygraphus, and Scolytus, to lightly or non-pigmented and consequently indistinct in the r-emadndng genera studied. Q.. valens has a small sclerot1zed, amber-coloured plate lateral to each of the pronotal plates discussed above (fig.90).
In immature larvae, the thorax and abdomen are usually nearly equal in diameter, with the exception of Scolytus piceae, where the thorax.is distinctly larger than the abdominal segments which taper toward the posterior end. As the larvae mature and reach the last instar and prepupaf stage, the developing wings and legs cause the thoracic - 47 - region to become enlarged, in particular forcing the development of distinct bulges or pedal lobes on the three thoracic sterna. The larva also decreases in length during the prepupal stage and becomes very white as feeding ceases and food is no longer visible in the alimentary canal. These changes will assist one in selecting mature larvae which, when available, are preferred for identification purposes.
The larvae of three species of Dendroctonus studied, valens, rufipennis and piceaperda. have distinctive integumental characteristics which separate them from the larvae of all other species studied and also can be used as key characters for the identification within the genus of the four species studied. The eighth and ninth abdominal segments of these species have strongly sclerotized, dorsal plates, brown or dark amber in colour. The dorsal plates of Q. valens are fused into a single, large plate which is armed with seven relatively
sharp projections (fig.38). The projections are in two transverse rows of three each and a single, median projection dorsal to the anus. In Q. rUfipennis and Q. piceaperda. there are single, dorsal plates on the eighth and ninth segments and a faint trace of a plate on the seventh
segment (figs.36 and 37). In Q. piceaperda, the sclerotized plates of the eighth and ninth segments are slightly rugose whereas those of Q. rufipennis have a pair of raised tubercles which are extremely rugose.
All three species have a sclerotized amber-coloured tubercle dorsal to the prothoracic and each abdominal spiracle (figs.32, 33 and 34). The spiracles are located in the ventral surface of the tubercle and are concealed when the larvae are viewed from above. The surface of the tubercle in Q. valens is slightly rugose whereas the outer portions of - 4a - the tubercles in rufipennis bear a number of discrete asperities which in piceaperda are joined to form a small but distinctly rugose area.
The dorsopleural lobe of abdominal segments one to eight, those with spiracles, of ~. valens and ~. rufipennis has a sclerotized, amber-coloured tubercle such as shown in figures 32 and 33. In Q. valens, the tubercles are large and extend beyond the spiracular tubercles when the larva is viewed from above. In~. rufipennis. the tubercles are smaller and are more in the form of a sclerotized area in the centre of the dorsopleural lobes. They do not extend beyond the s'piracular tubercles. The dorsopleural lobes of ~. niceaperda are not sclerotized and are not protuberent (fig.34). Q. simplex, the fourth species of the genus Dendroctonus studied, is readily separated fran the others by the absence of sclerotized plates on abdominal segments eight and nine and tubercles over the spiracles (fig.35).
The setal pattern of the larvae studied differs in certain respects between genera but is the same within genera with the exception of one species of Dendroctonus. Variations were found in number and position of setae between larvae of the same species but these were few and for the most part the setal pattern within species is constant.
Occasionally, minor variations between the arrangement, and, or position of setae on corresponding lobes or folds of two halves of a larva would destroy the symmetry, but these were the exception rather than the rule.
In the larvae studi.ed, the setal pattern of certain segments permitted grouping for comparative purposes. The setal pattern of the prothorax differs from that of the mesothorax and metathorax which are - 49 ..
alike. The first eight abdominal segments are similar except in
G. materiarius where the number of setae on the eighth segment differs from that on one to seven. The ninth and tenth segments have been considered separately. The arrangement of the setae on the
bo~ of Hylurgops pinifex is shown in figures 1" 2" 3 and 4.
Differences found .between this species and the other genera were in number, position and size. To facilitate comparison of the number of setae found on the larvae of different genera, the chart, shown as Plate XIV" was prepared. The left hand column lists the name applied to groups of setae or to lobes and folds of the body on which setae are -Loca t ed, divided into segments or groups of segments as discussed above. The names of the genera studied are arranged at the top of the chart as column headings and, where more than one species in a genus was studied, the number of species is inserted in brackets.
In a special column a t the left of the generic columns headed "Model No. of Setae", the .number of setae most commonly found on the larvae of the different genera has been inserted. Blank squares in generic columns indicate that the number of setae found on the larvae examined agrees with the standard number. Differences are reported by inserting the nl~ber of setae found in the respective square.
Examination of the chart shows that the setal patterns of'.
the different genera are relatively similar with the exception c£ the genus !E!. with five species stUdied" Trypodendron with one species and
Gnathotrichus with one species. The setal pattern of the five species of Ips was the same. It is perhaps not too surprising that the greatest variation occurred in the genera TtYpodendron and Gnathotrichus - 50 ... which, in a sense, are not true bark beetles but ambrosia beetles with quite different habitsfram the larvae of the remaining genera.
The number of setae which I found on the thorax and abdomen of larvae of Q. materiarius does not agree entirely with the findings of Schedl (1931) who studied the same species. However, when allowance is made for the two systems of nomenclature used, and different interpretations of certain areas of the body, the apparent conflictions reduce to a few minor differences in actual numbers of setae present. The numbers of setae found by Schedl, according to his nomenclature, as compared to the numbers I found, according to my terminology, are listed below:
'lhomas Schedl Prothorax:
Dorsal setae ••••••..•••••••• 12 Seta prescuti ••••••••••••••• 4) ) " scutuli •••••••••••••••• 3) ) •• 12 " hypopleuricum ••••••••••2 ) ) " epipleuricum ••••••••••• 3)
Mediosternal setae ...... 1 II sternalis ...... 1
Ventropleural setae •••••• 2) Laterosternal II ...... 3L 7 II sternellaris ...... 7 ) Pedal lobe setae ...... 2)
Mesothorax and Metathorax:
Setae on Dorsal Fold I ••••••• 4 Seta prescuti •••••••••••••• 4 " II " " II ...... 5 II scuttUi ••••••••••••••• 4) ).. 5 II epipleuricum •••••••••• 1) - 51 ...
Setae on alar area•••••..••••• 4 Seta hypopleuricum ••••••••• 4 Mediosternal setae ••••••••••• 2 " sternalis ••••••••••••• 2
Dorsopleural setae ••••••••••• 1) ) Ventropleural II · . 2) ) ••$ II sternellaris •••••••••• 7 Laterostemal II · . 3) ) Pedal lobe setae ...... 2)
Abdominal segments 1 to 7: Setae on Dorsal Fold I ••••••• 2 Seta prescuti ••••••••••••• 2
II " II II II ••••.• 4 II scutuli •••••••••••••• 4 Spiracular setae ••••••••••••• 2 " epipleuricum ••••••••• 2 Dorsopleural setae ••••••••••• 2 II hypopleuricum •••••••• 2 Ventropleural setae •••••••••• 2 " sternellaris ••••••••• 2
Mediosternal setae • •••• 3) ) ••• 4 " sternalis •••••••••••• 4 Laterosternal " • •••• 1)
Abdominal Segment 8: Setae on Dorsal Fold I ••••••• 2 Seta prescuti ••••••••••••• 2
.. II " .. III ..••• :3 II scutuli •••••••••••••• 2
Spiracular setae ••••••••••••• 2 II epipleuricum ••••••••• 3 Dorsopleural setae ••••••••••• 2 " hypopleuricum •••••••• 2
Ventropleural II ••••••••••• 2 II sternellaris ••••••••• 2 Mediosternal setae ••••••••••• 2) ) •• 3 II sternalis. ••••••••••• 4- Laterosternal II ••••••••••••1) - 52 -
Abdominal Segment 9: Dorsal setae .3 Seta prescuti ...... 2) ).. 3 " scutuli ...... 1)
Pleural setae •••••••••••••••• 2 II epipleuricum •••••••••• 3) ).. 4 II hypopleuricum ...... 1)
Sternal setae •••••••••••••••• 2 " sternalis ••••••••••••• 2) ).. 4 " sternellaris •••••••••• 2)
Abdominal Segment 10:
Anal setae ••••••••••••.•.•.•• 2 It analis •••••••••••••••• 2
The setae on the thorax and abdomen have not been used extensively in the keys prepared for identification of the larvae for several reasons. As explained previously, the numbers of setae are relatively constant within genera, and characters easier to utilize he. ve been found for generic identification. The bodies have to be specially prepared and stained to permit accurate determination of number and location of setae and even then the microscopic size of some setae, such as those on Trypodendron bivittatum and GnathotrichuB materiarius. increases the possibility of error. For purposes of checking certain determinations, the number of setae on all species studied can be found in the chart, Plate XIV.
The use of spiracles may add additional evidence to support or refute a determination of a genus arrived at from other characters.
Spiracles are located on the prothorax and first eight abdominal segments of scolytid larvae. They are of two types, first circular - 53 - as in figure 14, found in Fhloeosinus canadensis, Scolytus piceae,
T~podendron bivittatum and Gnathotrichus materiarius and second, a circular orifice with a pair of annulated air tubes lateral to the orifice (fig.13). The type of spiracle found in each genus studied is given in the generic descriptions but a few generaliz ations may be made here. The prothoracic spiracle is invariably larger than the abdominal ones and the first abdominal is usually, but not always, larger than those on segments two to eight. The length of the air tubes varies from approximately one-half to twice the width of the circular orifice. The usual position of the air tubes on the prothoracic spiracle is vertical while those on abdominal spiracles are usually postero-lateral except in Hylurgops, Dendroctonus and Ips where they are obliquely vertical with the extremities of the air tubes pointing posteriorly.
C. HEAD CAPSULE INCLUDING SETAL FATl'ERN
The head capsules with the mouthparts are, with a few exceptions, the only sclerotized parts of scolytid larvae and therefore offer more readily detected and permanent characters for separation of genera than do the soft bodies. The mouth parts will be considered individually in the sections following and the discussion here restricted to the value of head capsules alone in identification of larvae.
The head capsules of nearly all species studied were free as opposed to retracted, that is, t he entire or nearly the entire head capsule was visible with only a slight retraction into the folds of the prothorax. '!he head capsules of Pbloeosinus canadensis,
Trypodendron bivittatum and Scolytus piceae are exceptions to this - 54 - usual condition and are partially retracted into the prothoracic dorsum. In these retracted head capsules, dorsal epicranial setae
1 and 2 and the posterior epicranial setae are either located more anteriorly than in other species, as in f. canadensis and~. piceae
(figs. 17 and 19) or dorsal epicranial setae 1 and 2 have remained in the usual position but are greatly reduced in length as in 1. bivittatum (fig. 18).
Head capsules of representatives of the fifteen genera studied are shown in figures 6, and 17 to .31. The general shape varies frem those of the majority with curving sides, narrowly or broadly rounded posteriors, and which are approximately as broad as long, to those with sub-parallel sides, rounded posteriors and which are slightly longer than broad. The latter, represented by 2. piceae and f. canadensis (figs.19 and 17), appear much longer than wide but this is an illusion created by the sub-parallel sides and is not borne out by actual measurements of the length and width.
The shape of the frons is variable between genera, although always of the same general appearance. The posterior margin may vary from acute angled as in Hylurgops pinifex (fig.6) or Pityogenes hopkinsi (fig.25) to broad as in Gnathotrichus materiarius (fig• .31) or rounded as in Crypturgus atomus (fig. 28). '!he frons may be as broad as or broader than long. The mideranial suture is usually distinct extending from the posterior end of the frons anteriorly, approximately half the length of the frons. The surface of the frons may present features of value in identifying certain species. Larvae of Ips pini have a pair of small tubercles situated about midway of - 55 - the length of the frons (fig. 21) which are unique among those species studied. Mature larvae of H. pinifex have a median tubercle located at the anterior edge of the frons (figs. 6 and 8) which is not duplicated in other species. The surface of the frons of species of the genus Dendroctonus has transverse, rugose areas not found in other genera.
The antennae are small, consisting of a membranous basal portion with a ~entral, conical process. The basal section bears a number of setae, usually minute, but in certain cases one or more of these may be larger than the remainder. In~. piceae and ~. canadensis (figs. 19 and 17), one seta, mesad of the central cone, extends be,yond the tip of the cone.
With a few exceptions, the head capsules are amber or light brown in colour with darker areas across the anterior part of the frons and around the mandibular, articulatory processes. In~. piceae,
~. canadensis and I. bivittatum, the head capsule pigmentation is almost entirely lacking, a feature which readily separates these three from the remainder of the species under consideration. The pattern created by non-pigmented areas of the head capsule of G. materiarius is also distinctive (fig. 31). A pair of narrow, un pigmented bands, one on each side of the coronal suture and parallel . to it, runs posteriorly from the proximal region of the frontal suture.
A second pair extends from near the distal ends of the frontal suture postero-laterally to the sides of the cranium. In the genus Pityophthorus, there is occasionally an indistinct area on either side of the coronal suture beginning at the frontal suture which has less - 56 -
pigment than the remainder of the cranium (fig. 29).
The setae borne on the head capsule and mouth parts are more readily used in identification of genera than those on the thorax and abdomen largely because of the relatively greater size
of most of them. As was the case in the study of the integument,
the distribution of setae on the head capsules of species wi thin the same genus conformed to one pattern. A few differences occur
between genera as is apparent from figures 6 and 17 to 31. The distribution of setae and sensilla on the head capsules of the
fifteen genera studied is . compared in Table III below. It was found that eight genera, listed at the bottom of the table, had the same number of setae and sensilla and these common numbers have te en
inserted in column one of the table opposite the names given to them. Minor differences in numbers of setae and sensilla occurred in the
remaining seven genera and these have been noted in the appropria te squares under respective generic headings. Blank squares indicate that the number of setae or sensilla found agreed with the number common to all genera. Detailed information on the relative size and
conspicuousness of setae in the genera has been given in the generic descriptions in section VII of this paper. Minor variations in number and position of setae occurred occasionally between specimens of one species and the symmetry of the head capsules also was destroyed at times by the absence of a seta or the presence of an additional one. However, examination of a series of head capsules
of anyone species produced the figures given in Table III. The number of setae which I found on the head of g.materiarius - 57 -
differed from that reported by Schedl (1931) for the same insect. Many apparent differences are erased when the two systems of nomenclature used are compared but a few remain. The results I
obtained compared to those reported b,y Schedl are listed below.
Thomas Schedl
Dorsal epicranial setae•••• 13 - 17 Seta verto-mediana •••••• 12) ) It It -lateralis •••• 2) ••• 19 ) It geno-mediana ••••••• 5)
Lateral epicranial setae •• 2) ) •• 4 It geno-lateralis ••••• 6 Ventral It It ••• 2)
Frontal setae ••••••••••••••• 6-7 11 fronto-lateralis ••• 6) )... 7 It epistomalis •••••••• 1)
Not located It epicrano-lateralis•• 1
Posterior epicranial setae...... 5 Not shown
A number of specfnens of this species were examined and
considerable variation was found in numbers of setae in the dorsal epicranial group lateral to the coronal suture, the number ranging from 7 to 11, with 11 being most common. The number of setae on the
frons parallel to the frontal suture varied by 1, either 5 or 6 being
present, with 6 most common. The most anterior seta of this group,
mesad of the antenna, corresponding to the seta epistomalis of SChedl, was always present. The group of 5 setae lateral to the frontal suture, which I have included with the dorsal epicranial setae, would - 58 - represent the group of 5 called seta geno-mediana by Schedl. Similarly, the ventral and lateral epicranial setae correspond to
Schedl's geno-lateralis, although the number 5 I found disagrees with the 6 listed by Schedl., The 5 minute posterior epicranial setae, which I found on all head capsules examined, have not been listed by Schedl. No sensilla are listed by Schedlror are any sho~ on any of his figures. It is possible that certain of these were included as small setae.
The shape of the clypeus was generally quite similar in the species studied, broadly emarginate anterior margin and sides angular to broadly rounded (figs. 8 and 55 to 68). The anterior margin of species of the ~nus Pityophthorus (fig. 65) is more deeply emarginate than in other genera. '!be posterior edge of the labrum in most species is attenuated and is located below the anterior half of the clypeus. It is darkly pigmented and the shape of it when seen through the clypeus may lead one to think that the anterior margin of the clypeus is deeply cleft when such is not the case. There is usually a darkly pigmented band across the base of the clypeus, an area which has been indicated on the drawings by dotted lines. The shape and extent of the area may vary from a narrow band following the contour of the fronto-cly-peal suture as in Phloeosinus canadensis, Scolytus piceae, and Dryocoetes americanus (figs. 61, 62 and 63 respectively) to a wide band with a sinuate, anterior margin such as in Dendroctonus rufipennis or Ips perturbatus (figs. 55 and 58 respectively) • - 59 -
The elypeus of all spedes studied had two pairs of setae and a pair of sensilla located near the base. In the genera Dendroetonus and Pityokteines, clypeal seta 2, the outer of the two, varies from minute to less than one-half the length of seta number 1 (figs. 55 and 57 respectively). Considering the relatively great size of !2.. valens, Q. pieeaperda and Q. rufipennis compared to some seolytid larvae, clypeal seta 2 is indeed minute. In the figures of the clypeus of !2.. valens by Hopkins (1909), only a single seta is shown on either side of the elypeus and no mention is made of them in the text. In!2.. simplex, elypeal seta 2 is approximately one-half the length of seta number 1. In C£ypturgus atomus and Phloeosinus canadensis (figs. 56 and 61 respectively) both setae are equal in
length. In the remaining genera, elypeal seta 2 varies from one-half to slightly less than the total length of number 1. Schedl (1931) in his study of Gnathotrichus materiarius listed only one pair of setae on the clypeu5 whereas all the specimens I examined had two pairs, the outer seta being approximately one-half the length of the
inner one. - fIJ -
TABLE III Distribution of Setae and Sensilla on the Head Capsule
Dorsal epicranial setae 5 ~ 17
Posterior tt II 4 5 5 3 3 5 4-05 4-5 Lateral II " 2 Ventral II " 2 Frontal Setae 5 6 6-7 Dorsal epicranial sensilla 3 Posterior II " 1 Lateral " II 2 4 Ventral II II 1 Frontal " " 2
The following genera had the same number of setae and sensilla as listed in column 1 of the table. The number of species in each genus examined in this study is given in brackets after the generic name:
~rypturgus (1) PolygrPIlhus (1) Dendroctonus (4) Hylurgops (1) Trypodendron (1) Pityogenes (2) Pityokteines (1) Dryocoetes (2) - 61 -
D. LABRUM
The labrum is usually not as wide as the clypeus, broader than long, sides parallel or sub-parallel, anterior variable from broadly rounded as in Dendroctonus (fig. 55) or with a slight median protuberance on the anterior margin as in Pityokteines, figure 57. The posterior region of the labrum is attenuated and extends below the anterior end of the clypeus, being visible dorsally through the clypeus as a more darkly pigmented area. The outline of the posterior of the clypeus is indicated by a dotted line in figures 8 and 55 to 68 which are representative of the fifteen genera studied. The labrum is mostly uniformly pigmented with the exception of Phloeosinus canadensis and Scolytus piceae in which the labrum of each has an area at the posterior, indicated by dotted lines in figures 61 and 62 respectively, more darkly pigmented than the remainder. The outline of the tonnae is visible dorsally through the labrum and clypeus and has been indicated by dotted lines in figures 8 and 55 to 68. The free ends of the tormae are separate wi th the exception of Hylurgops pinifex, (fig. 8) where the posterior ends curve mesally and a weak line of fusion may occur, and in Trypodendron bivittatum (fig. 68) in which the posterior ends of the tonnae were fused in all the specimens examined.
With the exception of the labrum of Gnathotrichus materiarius (fig. 67) which has only a single pair of dorsal setae, all other species studied had three pairs of dorsal setae of which the median pair was longer than the other two pairs. Most species had a median and a pair of lateral sensilla on the labrum although these were frequently indistinct. - 62 -
E. EPIPHARYNGEAL LINING
The anterior margin of the labrum is reflexed and is continued dorsally into a semi-membranous lining of th~brum and clypeus extending into the oesophagus (figs. 16 and 69 to 89). Since there is no epipharynx in the sense that this term was first introduced into insect morphology, the inner surface of the labrum and clypeus has been called the epipharYngeal lining. This lining bears a number of setae, the number and arrangement of which are shown in figures 16, and
69 to 89. The reflexed anterior margin of the labrum bears two, three or four median setae in some cases. The majority of the species have only two of the antero-median setae with three present in the genera
Conophthorus and Pityophthorus, (figs. 73 and 74 respectively), and ibur in the species of Ips studied (figs.' 81 to 85)~ In the latter, the inner pair is large and stout while the outer two are much smaller, slender, and frequently difficult to see. On either side of the median setae, a group of three antero-lateral setae is present on all species studied with the exception of TryPodendron bivittatum (fig. 80) in which a single seta is present in the antero-lateral position.
The median epipharyngeal setae are usually in pairs located in median, long!tudinal rows anterior and or between the labral tormae.
Trypodendron bivittatum, figure 80, has no median epipharyngeal setae.
Three pairs of median epipharyngeal setae were found in the genera
Hylurgops. Crypturgus,Phloeosinus•. Conophthorus,Pityophthorus, Dryocoetes,
Polygraphus and Dendroctonus, figures 16, 69, 71, 73 to 78 and 86 to 89.
In Phloeosinus canadensis (fig. 71) the two anterior pairs are grouped around the antero-median setae giving a compact group of six setae. - 63 -
There are four pairs of median epipharyngeal setae in Scolytus piceae
(fig. 70) with the two anterior pairs arranged in a crescentic formation posterior to the antero-median setae. Orthotomicus caelatus (fig. 72) has a row of eight pairs of median setae aligned closely fran the anterior margin of the labrum to the posterior ends of the tonmae.
Ips was the only genus in which the number of median epipharyngeal setae varied between the species studied. Ips pini, and 1. borealis (figs. $1 and $4 respectively) had eight pairs of setae, whereas 1. calligraphus, I. perturbatus and I. chagnoni (figs. $2, $3 and $5) each had eleven pairs of median epipharyngeal setae. However, in the case of I. borealis, !. calligraphus and ! .. chagnoni, there was only a limited number of specimens available for examinat1 on, and a longer series might not support the figures obtained.
Considerable variation in the number and position of the median epipharyngeal setae was noticed in the specimens of Gnathotrichus materiarius examined. '!he arrangement shown in figure 79, with two anterior pairs of setae, two single sensilla in vertical alignment followed by two setae in vertical alignment and finally two more aensd.Ll.a, occurred most commonly. This arrangement does not agree with that found by Sched! (1931) who shows an anterior pair of setae or apical papillae and a median row of sensilla.
The surface of the epipharyngeal lining of all the species studied with the exception of Crypturgus atomus and TryPodendron bivittatum bears sensilla, either singly or in clusters along with the median epipharyngeal setae. - 64 -
F. MANDIBLE
The use of mandibular characteristics for taxonomic
purposes should be approached with caution since, by the time the larvae have matured, and it is at this time that the larval key is generally used, t he teeth are worn away and do not present the same clearly defined characteristics found at the beginning of a stadium. The characters discussed here and shown in figures 91 to 104 are those found on mandibles from newly moulted Lnatar-s ,
One species, Sco1ytus piceae (fig. 93) has only two incisoral teeth. Hy1urgops pinifex (fig. 105) has three incisora1 teeth and a minute fourth tooth near the middle of the incisora1 edge of the mandible, and the remainder of the species studied have three incisoral
teeth only. The genera in this latter group may be sub-divided into those in which the apical and sub-apical teeth are acute and the third tooth is emarginate, Ips, Pityogenes, Dryocoetes, Dendroctonus and Orthotomicus, (figs. 91, 92, 96, 103 and 104 respectively), and those in which all three teeth are acute, Crypturgus, Polygraphus, Trypodendron, Pityophthorus Phloeosinus, Gnathotrichus, ConophthoruB and Pityophthorus (figs. 94, 95 and 97 to 102 respectively). The dorsal surfaces of the . mandibles of certain species were smooth while others were rugose or bore transverse ridges. The distal half of the mandible of Polygraphus rufipennis is slightly less thick than the basal half, giving the effect of a ridge across the middle (fig. 95). In Pityokteines sparsus, there
is a transverse ridge across the centre of the dorsal surface (fig. 98).
The mandibles of all species examined had two dorsal setae - 65 - and three sensilla. A single sensillum is present on the inner dorsal surface and two sensilla, usually in close proximity to each other, near the basal edge of the dorsal surface. The arrangement of the setae divides the fifteen genera into two classes. In the genera Gnathotrichus, Conophthorus, Pityophthorus, Dendroctonus and Hylurgops (figs. 100 to 103 and 105 respectively), the setae are in vertical alignment, whereas in the genera ~ Pityogenes, Scolytus, Crypturgus, Polygraphus, Dryocoetes, Trypodendron, Pityokteines, Phloeosinus and Orthotomicus, (figs. 91 to 99 lind 104 respectively), the setae are close together and arranged more or less horizontal~.
G. MAXIU.A
The maxillae of all the species studied resemble each other fairly closely and offer only a few characters suitable for separation of genera and species.
The usual colour is a uniformly distributed amber or light brown with the exception of Phloeosinus canadensis and Scolytus piceae in which a section of the ventral surface of the stipes is non-ptgmented,
In f. canadensis (fig. 44) the non-pigmented area occupies nearly the entire length of the stipes and has stipital seta 1 located at its anterior end and a sensillum near the posterior end. The non-pigmented area in 2' piceae (fig.45) is small and medially located with stipital seta 1 in it, but the sensillum is more posterior in the pigmented area of t he stipes. - 66 -
The palpi are two-segmented and similar in most respects in all species studied with the exception of Pityogenes, Conophthoru8 and some species of the genus Pityophthorus. These have an accessory process on the outer distal part of the first segment of the palpus, approximately equal in length to the second segment of the palpus (figs. 46 and 51). The process occurs commonly on specimens of
Pityogenes hopkinsi, E. plagiatus and ~. resinosae, and less frequently on specimens of ~. coniperda and of the genus Pityophthorus.
The number of setae and sensilla present on the stipes, palpifer, lacinia and palpus was similar in those species studied.
Some variation in position of the stipital and palpiferal setae occurs between species as examination of figures 46 to 54 will show. Stipital seta 1 is usually located in the proximal third of the stipes but is found about the midpoint in Gnathotrichus materiarius and Scolytus piceae, and in the distal third of the stipes in Phloeosinus canadensis and I. bivittatum. Palpiferal seta 1, the outermost of the two, may be located on the edge of or in the membranous area at the base of the pal.pus , The inner palpiferal seta, number 2, is usually located in the membranous area but occasionally may be on the edge of the membrane in the sclerotized area as in Dendroctonus piceaperda (fig. 41).
H. LABIUM
Variations in the shape of the premental sclerite, the position of the postlabial setae, and the number of segments in the palpi, provide many of the characters used in the key to genera in section VII. A complete description of the labium of each genus is - 67 - given in the generic description but a few generalizations on the structure may be of value.
The fifteen genera can be divided into three groups on the basis of the shape of the premental sclerite. In the first group, the proximal part of the sclerite is attenuated to form a distinct projection more or less equal in width, for at least part of the distance it projects from the base of the sclerite, as in figures 45 and 46. Included in this type are the genera Hylurgops, Dendroctonus, Crrrturgus, Polygraphus, Phloeosinus, Scolytus and Pityogenes (figs. 9 and 41 to 46 respectively). In the second large group, the proximal part of thepremental sclerite is more in the fo rm of a triangle with the base of the triangle fonning the seat of the three anterior projections. In most of the genera of this group, !E!, Dryocoetes, Conophthorus, Pityophthoru5 and Gnathotrichu8
(figs. 49 to 53 respectively), the triangular formation is definite whereas the genera Orthotomicus and Pityokteines (figs. 47 and 48) exhibit a gradation from the shape in group one to that typical of the second group.
The third type of premental sclerite is found in the genus !rYpodendron only (fig. 54). The sclerite has three anterior projections as in groups one and two but the proximal part is roughly rectangular in shape, occupy ing the greater part of the postlabial region.
In certain genera of groups one and two, there is a median band extending from the end of the posterior projection, either part or all of the distance toward the tip of the median anterior projection, which is more darkly pigmented than the remainder of the sclerite. This may lead to a false impression of the true shape of the sclerite since frequently the areas lateral to t he dark area are indistinct. This was - 6$ -
found to be the case in the labimn of Orthotomicus caelatus in particular.
The labial palpi are two-segmented in all but three genera,
Pityophthorus, Conophthorus and Gnathotrichus, figures 51 to 53 respectively.
The nmnber of labial setae present in all genera studied was the same with the exception of Trypodendron. In this genus, a nmnber of the specimens examined had a supernumerary, postlabial seta lateral to postlabial seta 1 and this has been indicated by dotted lines in figure 54. The arrangement of the three postlabial setae can be used to group certain of the genera. In the genera which fell into group two on the basis of the shape of the premental sclerite, it was found that the postlabial setae in each were arranged in an approximately straight line with the distance between setae 1 greatest. The line proceeded antero-mesally ending with the least distance between setae number 3 as in figures 47 to 53. The arrangement of the postlabial setae is more varied in the genera assigned to group one on the basis of the shape of the premental solerite. In the genera Hylurgops, Dendroctonus and Polygraphus (figs. 9, 41 and 43 respectively), the three setae are arranged in the form of a triange with the greatest distance between setae 2 and the least distance between setae 1. This arrangement in the genus Polygraphus is particularly valuable in separating the larvae of f. rufipennis and Dryocoetes affaber, which are frequently found together, since the postlabial setae of ~. affaber are arranged as described for group number one, similar to that shown for ~. americanus (fig. 50). The postlabial setae of the genus Pityogenes (fig. 46) have the straight-line arrangement - 69 - typical of the second group. The arrangement of these setae in the genera Phloeosinus and Scolytus (figs. 44 and 45) is the reverse of that for group two. Beginning at the posterior end the distance separating setae 1 is the least and the line proceeds antero-laterally with the greatest distance occurring between setae 3. In the genus
Crypturgus (fig. 42), the three postlabial setae are arranged in a crescentic line with the greatest distance occurring between setae number 2. The postlabial setae of TryPodendron bivittatum (fig. 54), which is in a group by itself on the basis of the shape of the premental sclerite, has the setae arranged somewhat similar to that of Hylurgops and Dendroctonus. Seta number 1 is located on the postero-lateral areas of the premerItal sclerite with seta 2 and 3 close to the base of the lateral, anterior projections. The distance between setae 2 is greatest and seta
2 is also much closer to number 3 than to number 1.
The number of setae found by Schedl (1931) on thelabium of Gnathotrichus materiarius differs from that which I located on specimens of the same species examined during this study. Schedl shows two setae occurring in the areas between the median and lateral anterior projections of the premental sclerite, the anterior one of the two being quite short, and a single sensillum occurring where the basal segment of the palpus is usually located. In the specimens I examined, the reverse of this situation was found, a single seta but two sensilla where the basal segment of the palpus is normally found. It is possible that in the specimens examined by Schedl, one of the sensilla had developed into a small seta or was mistaken for a seta. On rare occasions it was noticed that an extra seta would be found on a specimen in a position normally - 70 -
occupied by a sensilltml. Where I found two 6 ensilla at t he base of the lateral anterior projection of the premental sclerite (fig. 53), Schedl located one sensillum and one seta.
VII. IDENTIFICATION OF GENERA AND SOME SPECIES STUDIED
This study was undertaken for the purpose of determining whether or not a satisfactory method could be devised for identifying the larvae of species of bark beetles when adults were not available or, when adults were available, to fortify cases of doubtful identification made from adult characteristics. It was realized that larval identifi cation alone might prove impractical but when taken together with other information already available, such as keys based on adult characteristics, host specificitishown by many species and characteristic gallery construction, a useful contribution would have been made to the tools at hand for taxonomic work in this group of insects. Working with a limited number of species from eastern Canada, it is considered that the objective has been satisfactorily attained to a certain degree.
A key, based on larval characteristics, has been prepared with which it is possible to detennine to the genus thirty species representing the fifteen ~nera studied. Fortunately, of the fifteen genera available for study, seven are represented by one species only in eastern Canada so the generic key is in reality a specific key. These genera are Crypturgus, Gnathotrichus, Hylurgops, Orthotomicus, Phloeosinus,
Pityokteines, and Polygraphus. One genus Scolytus, has only one species breeding in coniferous trees in eastern Canada and therefore, the generic key is a specific key also for all practical purposes. The remaining seven - 71 -
genera are represented by more than one species 50 the generic key is a key to genera only based on those species available. Of these seven genera, all species represented in eastern Canada in four of them,
Dendroctonus. Dryocoetes, Pityogenes and Conophthorus, were available for study. Only in the genus Dendroctonus was it possible to separate all the four species concerned on larval charaeteristics. In the genus ~ in which five species were available, it was only possible to carry the specific determinations to the point of separating Ips pini from all others. The present study has proven that anatomieal characters can be used successfully t 0 separate scolytid larvae at least to the genus, and further in certain cases, and, when additional species become available for study in the next few years, the study begun here can be extended and completed.
The keys have been prepared using mature and prepupal larvae for the most part since, at the, time the keys will be required, it is these stages which are most likely to be found. The mature larvae of course are easier to examine. To test whether the characteristics of mature larvae were also present in younger larvae, two species were checked. Larvae of Ips pini of varying sizes ranging from very minute, probably first instar, to prepupae were examined and no anatomical differences noted. This species can be identified in the larval stage by the presence of a pair of tubercles on the frons and these were present on the smallest sized larvae examined although not as apparent as in mature larvae. Larvae of Hylurgops pinifex were also examined and the setal pattern on the head, mouth parts and body was the same on all sizes of larvae checked. The only anatomical difference noted was tm - 72 -
absence of the median tubercle fran the frons on some of the very
small larvae. This tubercle is usually quite evident in the mature
larvae.
In most published keys to coleopterous larvae, the families
Scolytidae and Curculionidae are grouped and the claim is either made or
inferred that the larvae of these families cannot be separated on
anatomical characters. This may be true if the families are considered
as a whole and, until an examination of most of the species in both
families has been made, it will be impossible to say definitely that
they can or cannot be separated, since the larvae of both families do
resemble each other very closely. However, it has been shown qy certain authors that in specific cases scolytid larvae can be separated from
curculionid larvae in association with them. Wallace and Beard (1942)
described a method of separating the larvae of two species of bark
beetles, Scolytus multistriatus Marsh. and Hylurgopinus rufipes Eich.,
from two species of weevils, Magdalis armicollis Say and !1. barbita Say,
which frequent~ occurred together in the bark of elm trees. As further
evidence, I have been able to separate larvae of three species of weevils found in association with scolytid larvae in the bark of white
and jack pine, and white spruce. In white pine, a species of Pissodes
was found associated with Hylurgops pinifex, Orthotomicus caelatus,
~ pini and Dendroctonus valens. A second weevil, a species of Pissodes, was found in jack pine associated with species of Pityophthorus. Larvae of both of the species of Pissodes have distinct eye spots lateral to the antennae (fig. 39) and so are readily separated from the scolytid larvae concerned, which do not have -eye spots. Abdominal segments tlolO - 73 -
to seven of the weevil larvae have four dorsal folds in the integument (fig. 40) which also distinguishes them from scolytid larvae which have only three dorsal folds in those segments. In the trunks of white
spruce, weevil larvae of an undetermined species were conmonl.y found associated with the larvae of Dendroctonus piceaperda and Ips perturbatus. This species of weevil had no eye spots to separate it from associated scolytid larvae but again the abdominal segments two to seven had four dorsal folds contrasting with the three dorsal folds in these segments
in the two species of scolytids. There will probably be other instances of weevil and scolytid larvae occurring together which can be separated in specific cases. No general characteristics are available as yet to make a clear distinction between curculionid and scolytid larvae and
the best we can hope to attain is a solution to specific problems
involving a limited number of species.
Keys to the larvae of superfamilies of the order Coleoptera may be found in BOving and Craighead (1931) and the following key contain ing pertinent references to the families Curculionidae and Scolytidae of the superfamily Curculionoidea has been taken fram this publication.
Key t 0 families and subfamilies of Curculionoidea
1. Mentum portion of fused sub-facial region free laterally; legs present, but small and usually two-jointed••.•••••••••••••Brenthidae.
Mentum connected laterally with maxillary stipes; legs absent; pedal lobes, occupying their place, often bulging••••••••••••••••••2 - 74 -
2. Head capsule elongate, broadening posteriorly, and with straight
sides. (Head deeply retracted; spiracles uniforous with the
mouth-piece equipped with a spoutlike prolongation) ••••••Protohinidae.
Head capsule narrowing posteriorly, and with curved sides••.••••••••3
3. Abdominal hypopleurum subdivided into at least two lobes, one
superposed upon the other ••••..••••.•••••.•..••.•...•.••..•...... ••7
Abdominal hypopleurum not subdivided .••.•••....••.••••••.•••••.••••4
4. Abdominal segments with no more than two transverse, dorsal plicae 5
Abdominal segments with three or four transverse, dorsal plicae ••• 6
5. (Not applicable)
6. Spiracles on second to seventh abdominal segments not projecting
and not placed dorsally •••••••••••••••• Curculionidae and Scolytidae.
Since the above key will not separate weevil and scolytid larvae, one must now depend upon additional infonnation such as the location in which the larvae were found, gallery characteristics, and any other information which might be available to decide if the larvae belong to Curculionidae or Scolytidae. As discussed earlier in this section, in isolated cases it may be possible to tell from anatomical differences to which family the larvae belong. Assuming that we know that the larvae are those of species of bark beetles, the following keys which I have prepared as a result of a study of the external anatomy of thirty species of bark beetle larvae, can be utilized to determine the genus and in certain cases the species involved. - 75 -
Key to Genera
1. Proximal part of the premental sclerite of the labium triangular, (figs. 52, 53) or is a distinct projection of the main body of
the sclerite (figs. 45,46) 2
Proximal part of the premental sclerite broadly rectangular, lightly pigmented (fig.54) ••••••••••••••••••••••••••.•• TrYpodendron
2. Postlabial setae arranged in the form of a triangle, setae of middle pair farthest apart (figs.9,41) ••••••••••••••••••••••••.•••3
Postlabial setae not arranged as above•••••••••••••••••••••••••••••6
3. Postlabial seta 2 closer to number 3 than to number 1, large
species (figs.9, U) 4
Postlabial setae equally spaced or number 2 only slightly closer to number 3 than to number 1, small species (figs.42,43)••••••••••••••5
4. A single tUbercle located on the median anterior margin of the frons
in mature specimens (fig. 6) •••••••••••••••••••••••••••••• HylurgoPB
No tUbercles located on the frons •••.••.•••••••••••••• Dendroctonus
5. Posterior of the frons rounded, frontal setae 1 and 2 close together and located near the posterior, frontal sutures indistinct, very small species (fig.28) •••••••••••••••••••••••••••••.•Crypturgus
Posterior of the frons acute, frontal seta 2 located one-half the distance between 1 and 4, frontal sutures distinct, larger species
(fig.27)...... •...... Polygraphus - 76 -
6. Postlabial setae arranged in a straight or slightly crescentic line proceeding from seta number 1 antero-laterally, the distance between setae number 1 less than that separating either of the other two pairs of setae (figs.17 and 19) •••••••••••••••••••••••••••••• 7
Postlabial setae arranged in a s~raight or slightly crescentic line proceeding from seta number 1 antero-mesally, the distance between
setae number 1 greater than that separating either of the other two pairs of setae (figs. 46,47) •••••••••••••••••••••••••••••••••••.•• 8
7. A non-pigmented area occupies at least two-thirds of the ventral surface of the maxillary stipes; the lateral anterior projections of the premental sclerite of the labium join the base of this sclerite obliquely (fig.44) ••••••••••••••••••••••••••••••••••.••• Phloeosinus
The non-pigmented area occupies less than one-third of the ventral surface of the maxillar,y stipes; the lateral anterior projections of the premental sclerite of the labium join the base of this
sclerite at right angles (fig. 45) ••••••••••••••••••••••••• Scolytus
8. Dorsal epicranial setae of the head capsule in excess of 5
(fig. 31) Grlathotrichus
Dorsal epicranial setae of the head capsule 5 or fewer in number •• 9
9. Labial palpus apparently one-segmented (figs.5l,52)•••••••••••••• 10
Labial palpus distinctly two-segmented••••••••••••••••••••••••••• 11 - 77 -
10. Anterior margin of the clypeus usually deeply emarginate; darkly pigmented area at the base of cLypeus narrow, tormae slender (fig.65) usually three laterosternal setae on thoracic
segments...... ••.••...•••..•...... Pityophthorus
Anterior margin of the clypeus broadly emarginate,darkly pigmented band at base of clypeus narrow in the middle increasing to almost
a third of the depth of the clypeus on either side, tormae stout
(fig.66) usually four laterosternal setae on the thoracic segments , larger species, cone boring •••••••••••••••••••••••••• Conophthorus
11. Three pairs of median epipharyngeal setae (figs_ 73, 76 and 77) •• 12
More than three pairs of median epipharyngeal setae (figs.72,8l) 14
12. Clypeal seta 2 minute, much shorter than seta number 1 (fig.57) ; a narrow non-pigmented strip beginning at the frontal suture extends parallel to and on either side of the coronal Buture (fig. 24) ••••• •••••• Pityokteines
Clypeal seta 2 approximately one-half the length of seta number 1 (figs.60,63) dorsal epicranial area evenly pigmented•••..••••••• 13
13. Posterior projection of the premental sclerite of the labium distinct from the body of the sclerite for at least one-third of the total length of the sclerite (fig.46) ••••••••••••••••••••••••• Pityogenes
Posterior of the premental sclerite is triangular in shape
(fig. 50)...... Dryocoetes - 7a -
14. Antero-median setae of the labrum four in number, the outer pair
shorter and more slender than the inner pair (figs.al to 85) ••• Ips
Antero-median setae of the labrum two in number (fig. 72) ••••••••••
••••••••• Orthotomicus
In the preceding key it was, of course, impossible to include all the features which characterize the species examined in a particular genus. Therefore, it is now proposed to describe briefly the
chief anatomical features applicable only to the species studied. Where it has been possible to separate all or part of the species of a genus on the basis of anatomical characters, keys will be provided for this purpose. UnforttUlately, in most of the genera in which more than one species occurs in eastern Canada, it has not been possible to separate
them using the external anatom;y. Where this occurs, it is hoped that
the supplementary information given in this and the following sections on gallery characteristics, host specificities and average lengths of the larvae and corresponding adults will be of some assistance in carrying the identification beyond the generic level. The arrangement followed is alphabetical rather than the order in which the genera have been keyed out.
Conophthorus coniperda
II resinosae
These two species are the only ones in the genus listed by
Swaine (19la) as occurring in eastern Canada. They bore in the green
cones of white and red pine, Q. coniperda in white pine and Q. resinosae - 79 - in red pine. Swaine reports that occasionally Q. coniperda may be found in the buds and small twigs of white pine. It was not possible to separate the larvae of these two species on the basis of external anato~. It was noted that the accessory process on the outer, distal margin of the first segment of the maxillary palpus (fig. 51) occurred more frequently on Q. resinosae than on Q. coniperda, in the specimens examined. However, if the source of the larvae being examined is known, one can be reasonably certain with which species one is working. The following larval description is applicable to both species.
Head Capsule: fig.JO. Head free, slightly longer than wide, widest at centre, sides curved, posterior margin narrowly rounded, light amber in colour, slightly darker on the anterior of the frons and around the oral foramen. Frons triangular, less than one-half the length of the head capsule. Coronal and frontal sutures distinct. Endocarinal line distinct, a shallow, longitudinal impression along the endocarinal line and part of the ecdysial sulcus. Antenna conical in a basal, membranous area with a number of basal setae, three mf which, laterad of the cone, are about one-third the length of the cone. Distribution of setae as in figure JO and Table III. Ventral epicranial setae 1 and 2 both long and conspicuous.
C1yPeus: fig. 66. Sides rounded to angulate, anterior margin broadly emarginate. Basal, pigmented band approximately one-third the depth of the c1ypeus laterally, deeply indented medially. Clypea1 seta 1 almost twice the length of 2. - 80 -
Labrum: Fig. 66. Sides sub-parallel, anterior margin broadly rounded, centre slightly protuberent. Tormae straight, rather stout. Three pairs of dorsal setae. One median and paired lateral sensilla.
Epipharyngeal lining: fig. 73. Three antero-median and three pairs of antero-lateral setae on the anterior margin. Three pairs of median epipharyngeal setae, equally spaced, most anterior pair longest, located immediately posterior to the three antero-median setae. A pair of sensilla between second and third pair of setae and posterior to the third pair of setae.
Mandible: fig. 101. Three incisoral teeth, apical and sub-apical acute, third acute to rounded. Two setae on the outer, dorsal surface in vertical alignment. A single sensillum on the mesal surface below the third tooth and two sensilla on the proximal margin of the dorsal surface.
Maxilla: fig. 51- Palpus two-segmented, segment one with a long seta and two sensilla.
An accessory process usually borne on the outer distal margin of basal segment of pa.Ipus, Distal segment with one sensillum and apical papillae. Stipital se'ta 1 just posterior to middle of the stipes. Two palpiferal setae located in basal, membranous area. Lacinial lobe with seven dorsal setae, a distal group of five ventral setae and a single, ventral seta and sensillum at the base of the free lobe. - 81 -
Labium: fig. 51. Posterior region of premental sclerite triangular, median longitudinal streak of darker pigment present, sides of median anterior projection sloping laterally from distal end. Palpus apparently one-segmented, basal segment usually indistinct. Distal segment with one sensillum, two sensilla in position where basal segment usually located. TWo pairs of setae and one pair of sensilla on the ligula. One pair of long, prelabial setae. Postlabial setae 1 to 3 arranged in a relatively straight line, proceeding antero-mesally with the distance between setae 1 greatest, all three setae equally spaced, setae 1 and 2 longer than 3, setae 1 usually not posterior to the premental sclerite.
Thorax and Abdomen: Body curved, head free, hypognathous. Dorsal and sternal plates of prothorax indistinct in unstained specimens. Spiracles with two annulated air tubes, slightly longer than the width of circular peritreme. Prothoracic spiracle larger than abdominal ones, first abdominal spiracle larger than those on segments two to eight. Air tubes of prothoracic spiracle vertical, remainder postero-lateral. Distribution of setae as in plate XIV, agrees with standard except for four latero-sternal setae in thoracic segments instead of three, three alar setae on mesothorax and metathorax instead of two.
Crypturgus atomus
This was the only species examined in the genus Crypturgus.
The average length of the larva of this minute species was 1.4 mm. ... 82 ...
compared to a length of approximately 1 rom. for the adult. The following description covers the main features of the larva.
Head Capsule: fig. 28. Head free to slightly retracted, as broad as long, sides and posterior margin rounded, light amber in colour, slightly darker on anterior margin of the frons and around the oral foramen. Frons broadly rounded posteriorly. Coronal and frontal sutures not too distinct. Endocarinal line approximately one-third the length of the frons. Antenna conical in a basal membranous area with four setae lateral to the cone and one seta mesad of the cone approximately one-half the length of it. Setal pattern as in figure 28 and Table III. Setae relatively conspicuous considering the minute size of the larva. Frontal setae 1 and 2 close together, lateral to the endocarinal line, distance between frontal setae 2 and 4 approximately twice that between 1 and 2. Ventral epicranial
2 minute, 1 much longer.
ClyPeus: fig. 56
Sides angulate to r-ounded; anterior margin slightly emarginate. Basal, pigmented band approximately one-third the depth of the clypeus with anterior margin usually straight. Clypeal setae 1 and 2 subequal, about one-third the depth of the clypeus.
Labrum: fig. 56. Sides sub-parallel, anterior margin broadly rounded. Tormae relatively straight. One median and paired lateral sensilla. Three pairs of dorsal setae. - 83 -
Epipharyngeal lining: fig. 69. A pair of antero-median and three pairs of antero-lateral setae on the anterior margin of the epipharyngeal lining. Three pairs of equally spaced, median epipharyngeal setae. Sensilla not apparent.
Mandible: fig. 94. Three incisoral teeth, all acute. Two setae medially located on dorsal surface, close, approximately horizontal. One sensillum on the mesal surface below the third tooth and two sensilla on the proximal margin of the dorsal surface.
Maxilla: fig. 42. Palpus two-segmented, segment one with a moderately long seta and two sensilla, two with a single sensillum and apical papillae. Stipital seta 1 in lower third of the stipes. Palpiferal setae near or on edge of the membrane at the base of the paLpue, Lacinial lobe with seven dorsal setae and a distal group of five ventral setae and a single, ventral seta and a sensillum at the base of the lacinial lobe.
Labium: fig. 42. Posterior region of premental sclerite distinct, median longitudinal streak of darker pigment present, sides of median, anterior projection slope laterally from distal end. Palpus two-segmented, each segment with a single sensillum on the ventral surface. Two pairs of short ligular setae and a pair of ligular sensilla. A pair of long, prelabial setae. Postlabial setae 1 and 3 arranged in crescentic formation with the distance between setae number 2 the greatest, all three setae 0 n either side equally spaced, setae land 2 longer than 3, setae 1 - 84 - posterior to the premental 5clerite.
Thorax and Abdomen:
Body curved, head free to partially retracted, hypognathous. Dorsal and sternal plates of prothorax indistinct in unstained specimens. Spiracles indistinct, a circular peritereme with two annulated air tubes longer than the width of the peritreme •. Air tubes of pro thoracic spiracle vertical, those of abdominal spiracles postero lateral. Setae relatively long considering the minuteness of the larva. Setal pattern a s in plate XIV, agrees with standard with the exception of the pedal lobes which have three, occasionally four, setae.
Dendroctonus piceaperda
It rufipennis
It simplex
II valens
These four species of the genus Dendroctonus are found in coniferous trees in eastern Canada. This was the only one of the genera studied, having more than one species, in which all the species can be readily separated on the basis of anatomical characters. The following key will separate the four species of the genus:
1. Eighth and ninth segments bearing dorsal plates (figs. 36, 37 and 38); spiracles in ventral surface of a sclerotized tubercle
(figs... 32, 33 and .34) 2
Eighth and ninth segments without dorsal plates; no sclerotized
tubercles dorsal to the spiracles (fig. 35) ••..•.•••••••.•• simplex - 85 ..
2. Dorsal sclerotization of the eighth and ninth segments continuous, armed with seven spines (fig. 38) •••••••••••••••••••••••••• valens
Dorsal sclerotization of the eighth and ninth segments two
separate plates, not armed with spines •••••••••••••••••••••••••• ~3
3. Dorsal plates of the eighth and ninth segments bear a pair of rugose tUbercles (fig. 36); dorsopleural lobes of abdominal
segments one to eight are sclerotized and pignented (fig. 33)
..••••••••••'.••••••.•.••.•••••••.••.•••••••••••••••••. .. rufif)enni s
Dorsal plates of the eighth and ninth segments without definite, raised tubercles (fig. 37); dorsopleural lobes of the abdomen not sclerotized or pigmented (fig. 34) •••••..•••..•••••• piceaperda
With the exception of the characters contained in the key, the anatomy of the four species generally conforms to t he following
description. Where specific differences occur, these are described.
Head capsule: fig. 23.
Head slightly retracted; in piceaperda and rufipennis slightly longer than wide, sides curved, posterior margin narrowly rounded; in simplex and valens broader than long, posterior margin broadly rounded. Dark
amber in colour, darker on anterior of frons and around the oral foramen. Frons triangular, posterior end generally acute, may be
slightly rounded, slightly convex, with indefinite transverse folds.
Coronal and frontal sutures distinct. &docarinal line distinct, approximately one-half the length of the frons. Antenna central cone with a basal, membranous area with a number of small, basal setae. - 86 ..
Distribution of setae on head as in figure 23 and Table III. All setae conspicuous with the exception of ventral epicranial setae 1 and 2 which are minute in all four species, and the posterior epicranial setae which are minute. Dorsal epicranial setae 2 posterior to 1 in all species.
Clypeus: fig. 55 Sides angulate, anterior margin slightly emarginate. Basal pigmented band approximately one-half the depth of the clypeus laterally, indented medially. Clypeal seta 2 minute except in simplex where it is approximately one-half the length of 1.
Labrum: fig. 55 Sides parallel, anterior margin broadly rounded, slightly protuberent in simplex. Tormae distinct, relatively straight except for in valens where they are slightly bowed • . Three pairs of long, stiff, dorsal setae. A single median and paired lateral sensilla.
Epipharyngeal lining: figs. 86 to 89 One pair of antero-median and three pairs of antero-lateral setae on the anterior margin. Three pairs of median epipharyngeal setae, short, stout, equally spacedj anterior pair in piceaperda incurved. A pair of sensilla between the second and third pairs of median epipharyngeal setae and posterior to the third pair of setae in simplex (fig. 86); one pair of sensilla, three in a cluster, between the second and third pairs of setae and two pairs of single sensilla posterior to t he third pair of setae in piceaperda and rufipennis (figs. 87, 88). One pair of sensilla, three in a cluster, between the second and third pairs of setae ... 87 ...
and one pair, two in a cluster, posterior to the third pair of setae in valens (fig. 89)
Mandible: fig. 103.
Three incisoral teeth, apical and sub-apical acute, third emarginate.
Two dorsal setae in vertical alignment. One sensillum on mesal surface below the third tooth and two on t he proximal margin of the dorsal surface.
Maxilla: fig. 41.
Palpus two-segmented, segment one with a short seta and two s ensilla , distal segment with one sensillum and apical papillae. Stipital seta
1 in the proximal third of the stipes. Outer palpiferal seta not in the membranous area, inner s eta on the edge of the sclerotized area in all species except simplex where it may be entirely out of the membranous area,
In valens. the inner palpiferal seta is in a portion of membranous area partially enclosed by the sclerotized margin. Lacinial lobe with seven dorsal setae and a distal group of five ventral setae and a single ventral seta and sensillum at the base of the free lobe.
Labium: fig. 41
Posterior region of premental sclerite distinct, median, longitudinal streak of darker pigment, present, sides of median anterior projection only slightly sloped. Palpus two-segmented, each segment with a single sensillum on ventral surface and a distal segment with apical papillae.
Two pairs of setae and one pair of sensilla on the ligula. One pair of relatively long prelabial setae. Postlabial setae 1 to 3 arranged in a triangular formation,' setae 1 separated by the least distance and 2 by - 88 - the greatest distance, seta 2 closer to 3 than to 1, seta 1 and 2 longer than 3, setae 1 posterior to premental sclerite.
Thorax and abdomen: Body in simplex and piceaperda curved, head hypognathous, straighter and tending to be prognathous in valens and rufipennis. Dorsal plates of prothorax distinct except in simplex. In valens, a small sclerite located lateral to each larger dorsal plate of the prothorax (fig. 90). Dorsopleural lobes of abdominal segments one to eight sclerotized and amber coloured in valens and rufipennis, not so in piceaperda and simplex (figs. 32 to 35). Q. valens with a single, heavily sclerotized dorsal plate on segments eight and nine armed with seven spines (fig. 38), spines arranged in two transverse rows of three each and a single, median, spine over the anus. Q. rufipennis and piceaperda with separate dorsal plates on segments eight and nine and a faint trace of a plate on segment seven (figs. 36 and 37). Dorsal plates of rufipennis each with two raised tubercles, extremely rugose; only a slight indication of a pair of tubercles in piceaperda. Q. simplex without dorsal plates. Spiracles in all but Q. simplex borne on ventral surface of sclerotized,amber-coloured tubercles (figs. 32, 33 and 34); tubercles in rufipennis with a number of discrete asperities on the surface, the asperities in piceaperda coalesced, presenting a small rugose area. Spiracles in simplex smaller than in other species, anriulated air tubes shorter than width of peritreme. Setae conspicuous in all but simplex and distribution as in plate XIV.
Setal pattern as in the standard except for three to four setae on the pedal lobes of the thorax in place of two, six dorsal setae in place of five on the ninth segment of the abdomen except for rufipennis which has eight in this position.
Dryocoetes affaber
II americanus
The larvae of these two species could not be separated on the basis of anatomical characters, although mature larvae of Q. americanus are much larger than those of!2.. affaber. Both species are found chiefly in spruce although !2.. americanus has been recovered from the brace roots of white and red pine. !2.. affaber is more likely to be found associated with Polygraphus rufipennis than other species and these species can be separated on the characters given in the key to the genera. Q. americanus has usually been found in association with Hylurgops pinifex and Orthotomicus caelatus, particularly the second broods of these latter species. Again the separation of larvae of these genera can be made with the characters given in the key to genera. The following description of the larva is applicable to both species of Dryocoetes.
Head capsule: fig. 26 Head free, slightly longer than broad, sides curved, posterior margin narrowly to broadly rounded, dark amber to brown, darker on anterior region of frons and around the oral foramen. Frons triangular, posterior end acute. Coronal and frontal sutures distinct.
Endocarinal line distinct, extending approximately one-half the length of the frons. Antenna conical with a basal membranous area with several basal setae, three of which are approximately one-half the - 90 - length of the cone. Distribution of setae as in figure 26 and
Table III. All setae conspicuous with the exception of the posterior epicranial setae which are minute, and ventral epicranial seta 1, usually minute. Dorsal epicranial setae 1 and 2 either in a transverse row or 2 slightly posterior to 1.
Clypeus: fig. 63. Sides rounded to angulate, anterior margin broadly emarginate. Basal, pigmented band very narrow. . Clypeal seta 1 almost twice the length of 2.
Labrum: fig. 63. Sides sub-parallel, anterior margin broadly rounded. Tormae slender, slightly convex mesally. Three pairs of dorsal setae. One median and paired lateral sensilla.
Epipharyngeal lining: fig. 77. One pair of antero-median and three pairs of antero-lateral setae on anterior margin. Three pairs of median epf.pharyngeak eet.ae; equally spaced. A pair of sensilla anterior and posterior to the third pair o£ setae.
Mandible: fig. 96. Three incisoral teeth, apical and sub-apical acute, third emarginate. Two short setae on the dorsal surface close together and beside each other. One sensillum on the mesal surface and two sensilla on the proximal margin of the dorsal surface.
Maxilla: fig. 50.
Palpus two-segmented, segment one with a short seta and two sensilla, - 91 - segment two with one sensillum and apical papillae. Stipital seta 1 in proximal third of the stdpea, Pa1piferal setae in the membranous area at the base of the paLpus, Lacinia1 lobe with seven dorsal setae and a distal group of five, ventral setae and a single, ventral seta and sensillum at the base of the free lobe.
Labium: fig. 50. Premental sclerite triangular, posterior region slightly constricted, median anterior projection short and broad, a median, longitudinal streak of darker pigment present. Palpus two-segmented, basal segment with two sensil1a and distal segment with one sensillum and apical papillae. Two pairs of setae and one pair of sensilla on the ligula. One pair of long prelabial setae. Postlabial setae 1 to 3 in a straight line arrangement proceeding antero-mesally with the greatest distance between setae 1, setae 1 and 2 longer than 3, all setae equally spaced, setae 1 usually posterior to the premental sclerite.
Thorax and Abdomen: Body curved, head free, hypognathous. Dorsal and sternal plates of the prothorax distinct. Spiracles with two annulated air tubes longer than width of the peritreme, prothoracic spiracle larger than the abdominal ones, first abdominal spiracle only slightly larger than those on segments two to eight, air tubes vertical in position in prothoracic spiracle and postero-lateral in the abdominal spiracles. Distribution of setae as in plate XIV, agrees with the standard. Setae relatively conspicuous particularly on abdominal segments seven, eight and nine. - 92 -
Gnathotrichus materiarius
Gnathotrichus is one of the two ~nera of ambrosia beetles to be encountered in conifers in eastern Canada, and Q. materiariuB is the only representative of the genus in eastern Canada. If the habitat of the larvae being examined is known to be that of the ambrosia beetles, and the larvae are from conifers, then the species will be either in the genus Gnathotrichus or in Tqpodendron. The information given in the generic key together with the more detailed description of Q. materiarius following will pennit identification to species.
Head capsule: fig.3l Head free, slightly longer than wide, widest at the centre, sides curved, posterior margin broadly rounded, amber coloured with two non-pigmented areas on each half of the epicranium, beginning at the frontal sutures and proceeding posteriorly; one area parallels the coronal suture and the second is lateral to this on the side of the head capsule. Frons shield shaped, the posterior roughly transverse. Endocarinal line distinct, extending approximately one-half the length of the frons.
Antenna a central cone with basal membranous area with several small, basal setae. Distribution of setae as in figure 31 and Table III. Five or six pairs of sensilla. The most posterior setae arranged in a line along the frontal suture with a fifth seta mesad of the anterior one. The most anterior seta located near the antenna. The number of setae in the light-coloured stripe parallel to the coronal suture varies from seven to eleven with eleven being most common. A - 9.3 - second group of five dorsal epicranial setae located lateral to the frons. One sensillum lies between lateral epicranial setae 1 and 2 and a row of three sensi11a posterior to lateral epicranial seta 1.
All the head capsule setae with the exception of the five posterior epicranial setae large and conspicuous.
C1ypeus: fig. 67. Sides convex to angulate, anterior margin broadly emarginate. Basal, pigmented band approximately one-half the length of the clypeus laterally, indented medially. Clypeal setae land 2 sub-equal, 1 longer than 2 which varies from minute to approximately one-half the length of 1.
Labrum: fig. 67. Sides sub-Parallel, anterior margin rounded with a median protuberance.
Tormae long and slender. One pair of dorsal setae. One median and paired lateral sensilla.
Epipharyngeal lining: 79. One pair of antero-median setae and three pairs of antero-lateral setae, the outer pair very minute. Two pairs of median epfpharyngeal, setae with two sensilla posteriorly, followed by two setae in vertical alignment; posterior to these are two additional sensilla.
Mandible: fig.lOO Three incisoral teeth, all acute. Two dorsal setae in vertical alignment, widely separated. One sensillum on the mesal surface and a pair of sensilla on the proximal margin of the dorsal surface. - 94 -
Maxilla: fig.53 Palpus two-segmented, segment one with a short seta and two sensilla, segment two with one sensillum and apical papillae. Stipital seta 1 just posterior to middle of the stdpea, Outer palpiferal seta in the sclerotized margin of the basal membrane, inner palpiferal seta in the membranous area at the base of the palpus. Lacinial lobe with seven short, dorsal setae and a distal group of five, ventral setae and a single ventral seta and sensillum at the base of the free lobe.
Labium: fig. 53. Characterized by the broadly rounded anterior aspect of the combined prementum and ligula. Median anterior projection of the premental sclerite short, the sides of the sclerite curved, ending posteriorly in a triangular shape, apex acute. Palpus one-segmented, two sensilla where the basal segment of the palpus usually located. Distal segment with one sensillum and apical papillae. Two pairs of short setae and one pair of sensilla on the ligula. A pair of moderately long prelabial setae. Postlabial setae 1 to 3 in a straight line arrangement proceeding antero-mesally with the greatest distance between setae 1; all setae equally spaced, setae 1 level with or anterior to t he end of the premental sclerite.
Thorax and abdomen: Body curved, head free, hypognathous. Dorsal and sternal plates on the prothorax indistinct. Spiracles circular, prothoracic one slightly larger than the abdominal ones which are equal in size. Distribution of setae as in plate XIV. Considerable variation occurs from the standard and, as well, the setal pattern on abdominal segment eight differs from that on one to seven. - 95 -
Hylurgops pinifex
Since a detailed description of the larva of this species has already been gi.ven, you are referred to section V for the information on larval characteristics.
Ips borealis
II calligraphus
II chagnoni
II perturbatus
II pini
Specimens of five of the eight species of the genus Ips reported as occurring in eastern Canada were available for study, although only a few specimens each of I. borealis, I. calligraphus and I. chagnoni. The larvae of all five species resemble each other quite closely with the exception of that of I. pini which has a pair of frontal tubercles separating it from the other species of Ips studied. It is interesting to note that the presence of these tubercles also separates I. pini from all others examined in this study. Anatomical evidence was insufficient to separate the remaining species of the genus Ips. The following description has been prepared from examination of larvae of the five species listed above.
Head capsule: figs. 21 and 22.
Head free, as broad as long, widest at the centre, sides curved, posterior margin broadly rounded, amber coloured, darker on the anterior part of the frons and around the oral foramen. Frons triangular, posterior end usually acute angled, I. pini with two elliptical tubercles centrally - 96 ... located on the frons (fig. 21). Coronal and frontal sutures distinct. Endocarinal line distinct, approximately one-half the length of the frons. Antenna a central cone with a basal membranous area with several small, basal setae. Distribution of setae as in figures 21 and
22 of Table III. Setae relatively conspicuous with the exception of the posterior epicranial setae. Dorsal epicranial setae 1 and 2 on the same level or 2 slightly anterior to 1. Ventral epicranial setae sub-equal,
1 shorter than 2.
Clypeus: fig. 58. Sides rounded, anterior margin broadly emarginate. Basal, pigmented band with a sinuate anterior border, one-third to one-half the depth of the clypeus laterally and indented medially. ClyPeal seta 1 usually at least twice the length of 2.
Labrum: fig. 58. Sides sub-parallel, anterior margin slightly protuberent medially. Torma.e short, divergent posteriorly. Three pairs of dorsal setae. One median and paired lateral sensilla.
Epipharyngeal lining: fig. 58. Two pairs of antero-median setae, inner pair large, stiff, outer pair small, slender, usually indistinot. Three pairs of stout, antero lateral setae. Median epipharyngeal setae vary in munber, usually eignt pairs in I. pini and!. chapponi and eleven pairs in !. perturbatus. !. borealis and!. calligraphus. Position of sensilla among the median setae not constant. - 97 -
Mandible: fig. 91 Three incisoral teeth, apical and sub-apical acute to sub-acute, third emarginate. Two setae on dorsal surface, close together and • horizontally positioned. One sensillum on the mesal surface, one pair on the proximal margin of the dorsal surface.
Maxilla: fig. 91. Palpus two-segmented, segment 1 with a moderately long seta and two sensilla, segment 2 with one sensillum and apical papillae. Stipital seta 1 in proximal third of stipes. Outer palpiferal seta on the sclerotized border of the membranous area at the base of the palpus, inner seta in the basal membrane. Lacinial lobe with s even dorsal setae and a distal group of five ventral setae and one ventral seta and sensillum at the base of the free lobe.
Labium: fig. 49. Posterior part of premental sclerite triangular; median, longitudinal streak of darker pigment present, sides of median, anterior projection parallel. Palpus two-segmented, each segment with one sensillum in the ventral surface. Two pairs of setae and one pair of sensilla on the ligula. One pair of long prelabial setae. Postlabial setae 1 to 3 in a straight line arrangement proceeding antero-mesally with the greatest distance between setae 1, all setae equally spaced, 1 and 2 slightly longer than 3, setae 1 not posterior to premental sclerite.
Thorax and abdomen:
Body curved, head free, hypognathous. Dorsal and sternal plates of the prothorax relatively distinct. Spiracles with two annulated air tubes - 98 - equal to width of peritreme, prothoracic spiracle larger than abdominal ones, air tubes vertical, first abdominal spiracle about twice the size of those on segments two to eight, air tubes oblique in position, pointing posteriorly. Setae not too conspicuous, distribution as in plate XIV, indicating a few variations from the standard; one extra laterosternal seta on thoracic segments; three alar setae in place of two on the mesothorax and metat.horaxj on segments one to eight, one ventropleural seta in place of two but two laterosternal setae in place of one in the standard; four dorsal setae on the ninth abdominal segment opposed to five in the standard.
Orthotomicus caelatus
Q. caelatus is the only species in the genus reported in eastern Canada. It is usually found in association with species of Ips and Hylurgops pinifex from which the larvae can be separated on the basis of characters given in the generic key. The following description covers the main anatomical features of the larva:
Head capsule: fig. 20. Head free, as broad as long, widest at the centre, sides curved, posterior margin broadly rounded; amber coloured, darker on the anterior part of the frons and around the oral foramen. Frons triangular, posterior end acute angled. Coronal and frontal sutures distinct. Endocarinal line distinct, approximately one-half the length of the frons. Antenna a central cone with a basal, membranous area with several, small, basal setae. Distribution of setae as in figure 20 and Table III. Setae are distinct with the exception of the posterior - 99 - epicranial setae and ventral epicranial seta 1 which are minute.
Dorsal epicranial setae 1 and 2 in a transverse line or 2 slightly posterior to 1.
Clypeus: fig. 59. Sides angulate, anterior margin broadly emarginate. Basal, pigmented band approximately one-half the depth of the clypeu6 laterally, indented medially. Clypeal seta 1 approximately twice the length of 2, occasionally, seta 2 minute.
Labrum: fig. 59. Sides sub-parallel, anterior margin rounded. Three pairs of dorsal setae. One median and paired lateral sensilla. Tormae stout, diverging slightly posteriorly.
Epipharyngeal lining: fig. 72. One pair of short antero-median setae and three pairs of antero-lateral setae on the anterior margin. Eight pairs of median epipharyngeal setae between the tormae with one pair of sensilla posterior to the median setae.
Mandible: fig. 104. Three incisoral teeth, apical and sub-apical acute, third slightly emarginate. Two setae on the dorsal surface, c lose together and beside each other. One sensillum on the mesal surface and two s ensilla on the proximal margin of the dorsal surface. - 100 ..
Maxilla: fig. 47. Palpus two-segmented, segment one with a short seta and two sensilla, segment two with one sensillum and apical papillae. Stipital seta 1 in proximal third of the stdpea, Palpiferal setae on the sclerotized margin of the membranous area at the base of the palpus or the inner seta frequently in the membrane. Lacinial lobe with seven dorsal setae and a distal group of five ventral setae and one seta and sensillum at the base of the lobe.
Labium: fig. 47. Posterior part of premental sclerite triangular with part of it a distinct projection, a median, longitudinal streak of darker pigment present. Palpus two-segmented, each segment with one sensillum in the ventral surface and the distal segment with apical papillae. Two pairs of short setae and a Pair of sensilla on the ligula. One pair of long prelabial setae. Postlabial setae 1 to 3 in a relatively straight line arrangement proceeding antero-mesally with the greatest distance between setae 1, all setae equally spaced, 1 and 2 slightly longer than 3, setae 1 not posterior to premental sclerite.
Thorax and Abdomen: Body curved, head free, hypognathous. Dorsal and sternal plates of the prothorax only lightly pigmented, not too distinct. Spiracles with two annulated air tubes longer than the width of the peritreme, prothoracic spiracle larger t han the abdominal ones, air tubes vertical in position, first abdominal spiracle slightly larger than those on segments two to eight, air tubes postero-lateral in position. Distribution of setae on the body as in plate XIV, agrees with the standard. - 101 -
Phloeosinus canadensis
This is the only species in the genus reported in eastern
Canada. A knowledge of the source of the larvae being examined is particularly important here since f. canadensis is specific to eastern white cedar. It is also the only species of bark beetle reported as attacking this species of tree in eastern Canada which should confinn any identification made by use of the key. The following is the description of the larval anatomy.
Head capsule: fig. 17. Head retracted, slightly longer than wide, sides sub-parallel, posterior margin broadly rounded. Pigment absent over most of the head capsule except for light brown areas on the anterior region of frons and around the oral foramen. Frons triangular, posterior area acute angled. Coronal and frontal sutures indistinct. Endocarinal line indistinct. Antenna a central cone with a basal, membranous area with several, basal setae, one of which, mesad of the cone, exceeds the length of the cone. All setae minute and indistinct. The distribution of setae as in figure 17 and Table III. The arrangement differs considerably from the typical pattern for scolytid larvae. Dorsal epicranial setae 1 and 2 and posterior epicranial setae 1 to 3 are located ahead of the posterior angle of the frons.
Clypeus: fig. 61-
Sides angulate, anterior margin slightly emarginate. Basal pigmented band narrow, following the contour of the fronto-clypeal suture.
Clypeal setae 1 and 2 approximately equal in length. - 102 -
Labrum: fig. 61. Sides parallel, anterior margin slightly protuberent medially. Tormae long, slender. A narrow band at the posterior of the labrum more darkly pigmented than the remainder. Three pairs of long, slender, dorsal setae. One median and paired lateral sensi11a.
Epipharmgeal lining: fig. 71. A pair of short, antera-median setae and three pairs of long, antero lateral setae on the anterior margin•. Three pairs of median epipharyngeal setae, two pairs immediately posterior to antero-median setae, third pair between the tormae. One pair of sensilla anterior to and posterior to third pair of median setae.
Mandible: fig.99. Three incisoral teeth, apical and sub-apical acute, third triangular. Two setae on the outer dorsal surface, close together and beside each other. One sensillum on the mesal surface, two sensilla on the proximal margin of the dorsal surface.
Maxilla: fig. 44. Palpus two-segmented, segment one with a moderately long seta and two sensi11a, segment two with one sensillum and apical papillae. Approxi mately two-thirds the length of the ventral surface of the stipes not pigmented. Stipital seta 1 in the distal half of the stipes at the anterior end of the non-pigmented area, stipital sensillum at the posterior of the non-pigmented area. Palpiferal setae in the membrane at the base of the palpus. Lacinial lobe with seven dorsal setae and a distal group of five ventral setae and one ventral seta and one sensillum at the base of the free lobe. - 103 -
Labium: fig. 44. Posterior part of premental sclerite distinct, median anterior projection long and narrow, sides parallel; lateral, anterior projections with sides curving mesally at the posterior. Palpus two-segmented, each segment with one sensillum and the distal segment with apical papillae. Two pairs of setae and one pair of sensilla on the ligula. One pair of long, prelabial setae. Postlabial setae 1 to 3 in a straight line arrangement proceeding antero-laterally with the least distance separating setae 1; all setae equally spaced, setae 1 and 2 slightly longer than 3, seta 1 not posterior to the premental sclerite.
Thorax and abdomen: Head retracted, thoracic region of the boqy broader than the tapered abdomen. Dorsal and sternal plates of the pro thorax indistinct in unstained specimens. Spiracles, inconspicuous, circular; prothoracic spiracle larger than the abdominal ones; first abdominal spiracle slightly larger than spiracles on the remaining abdominal segments. Distribution of setae as in plate XIV, agrees with the standard except for three setae on the pedal lobes of the mesothorax and metathorax opposed to two in the standard. All the body setae small and relatively inconspicuous.
Pityogenes hopkinsi
II plagiatus
Anatomical evidence is insufficient to separate the larvae of these species. f. hopkinsi is found most commonly in white pine and f. plagiatus in red pine. '!he egg galleries and larval mines may be of - 104 - assistance in separating the species. Adults of E. hopkinsi cut the egg galleries transversely across the bark and the larvae mine with the bark fibres rather than across them. With E. plagiatus. the egg galleries radiate in all directions from the nuptial chamber, the egg niches are irregularly spaced in contrast to the closely spaced, more evenly arranged egg niches of E. hopkinsi. The following description is applicable to larvae of both species.
Head capsule: fig. 25. Head free, as broad as long, sides curved, posterior margin broadly rounded, amber coloured, slightly darker on the anterior part of the frons and around the oral foramen. Frons triangular, posterior acute angled. Coronal and frontal sutures not too distinct. Endocarinal line distinct, approximately one-half the length of the frons with a shallow depression along its length. Antenna a central cone in a basal, membranous area with several basal setae. Distribution of setae as in figure 25 and Table III. Setae are all approximately equal in length with the exception of the minute posterior epicranial setae. Ventral epicranial seta I shorter than 2.
Clypeus: fig. 60. Sides angulate, anterior margin broadly emarginate. Basal, pigmented band approximately one-half the depth of the clypeus laterally, indented medially. Clypeal seta 1 usually about twice the length of seta 2.
Labrum: fig. 60.
Sides parallel, anterior margin transverse to broadly rounded. Tormae slender, long. Three pairs of dorsal setae. One median and paired lateral sensilla. - 105 -
Epipharyngeal lining: fig. 75. A pair of antero-median setae and three pairs of antero-lateral setae on the anterior margin. Three pairs of median epipharyngeal setae, equally spaced with one pair of sensilla between the second and third pair of setae.
Mandible: fig. 92.
Three incisoral teeth, apical and sub-apical acute, third emarginate. Two setae on the dorsal surface close together and beside each other. One sensillum on the mesal surface and two on the proximal margin of the dorsal surface.
Maxilla: fig. 46.
Palpus two-segmented, segment one with a long seta and two sensilla. An accessory process located on the outer, distal margin of segment 1, approximately as long as the second segment. Segment two with one sensillum and apical papillae. Stipital seta 1 in the proximal third of the stipes. Palpiferal setae in the membranous area at the base of the palpus, Lacinial lobe with s even dorsal setae and a distal group of five ventral setae and one ventral seta and sensillum at the base of the free lobe.
Labium: fig. 46. Posterior part of premental sclerite distinct, anterior, lateral projections parallel, at right angles to the base of the sclerite, a median, longitudinal streak of darker pigment. Palpus two-segmented, each segment with one sensillum and the distal segment with apical papillae. TWo pairs of short setae and a pair of sensilla on the ligula.
A pair of long, prelabial setae. Postlabial setae 1 to 3 in a straight - 106 - line arrangement proceeding antero-mesally with the greatest distance between setae 1; all setae equally spaced, 1 and 2 slightly longer than 3, setae 1 not posterior to the premental sclerite.
Thorax and abdomen: Body curved, head free, hypognathous. Dorsal and sternal plates of the prothorax only ' lightly pigmented and indistinct. Spiracles with two annulated air tubes longer than the width of the peritreme. Prothoracic spiracle larger than abdominal ones, air tubes vertical in position, abdominal spiracles equal size, air tubes postero-lateral in position. Setae conspicuous, distribution as in plate XIV, agrees with the standard with the exception of three alar setae in place of two on the standard.
Pityokteines .spar sus.
Only one species of the genus Pityokteines is reported as occurring in eastern Canada and this bark beetle is the one most commonly found in balsam fir, a factor of considerable value in identifying specimens of this species if the host material is known. The following brief description is given of the larval anatomy.
Head capsule: fig. 24 Head free, slightly longer than wide, widest at the centre, sides curved, posterior margin narrowly rounded, amber coloured, darker on the anterior region of the frons and around th~ oral foramen. A narrow, elongated area on either side of and parallel to the ecdysial sulcus and extending from the frontal sutures about two-thirds of the distance to the posterior of the head capsule, with noticeably less pigmentation. Frons triangular shaped, sides crenulate in appearance caused by dilations in the frontal - 107 - sutures. Coronal and frontal sutures distinct. Endocarinal line distinct, extending approximately one-half the length of the frons.
Antenna a central cone in a basal, membranous area with several small setae. Setal pattern as in figure 24 and Table III. Ventral epicranial setae 1 and 2 equal in length but inconspicuous. Posterior epicranial setae minute. Dorsal epicranial seta 2 anterior to the line between dorsal epicranial setae 1.
Clypeus: fig. 57. Sides angulate, anterior margin slightly emarginate. Basal, pigmented band approximately one-half the depth of the clypeus laterally, deeply indented medially. Clypeal seta 1 long, 2 minute.
Labrum: fig. 57. Sides parallel, anterior margin protuberent in the centre. Tormae long, slender, slightly divergent posteriorly. Three pairs of dorsal setae.
One median and paired lateral sensilla.
Epipharyngeal lining: fig. 76. A pair of antero-median setae and three pairs of antero-lateral setae on the anterior margin. Three pairs of median epipharyngeal setae, equally spaced. One pair of sensilla between the second and third pair of setae and posterior to the third pair of setae.
Mandible: fig. 98. Three incisoral teeth all acutely rounded, third more rounded than the others. A transverse ridge across the outer dorsal surface. Two setae in a slight depression below the ridge on the dorsal surface, close together and beside each other. One sensillum on the mesal surface and two on the proximal margin of the dorsal surface. - 108 -
Maxilla: fig. 48. Palpus two-segmented, segment 1 with a short seta and two sensilla, two with one sensillum and apical papillae. Stipital seta 1 posterior to the
centre of the stipes. Palpiferal setae in the membranous area at the base of the palpus. Lacinial lobe with seven dorsal setae and a distal group of five ventral setae and one ventral seta and sensillum at the base of the lacinial lobe.
Labium: fig. 48. Posterior of premental sclerite triangular to partially distinct, median longitudinal streak of darker pigment present, sides of median, anterior projection nearly parallel. Palpus two-segmented, each segment with one sensillum and the second segment with apical papillae. Two pairs of
short setae and one pair of sensilla on the ligula. One pair of moderately long prelabial setae. Postlabial setae 1 to 3 in a straight line arrangement proceeding antero-mesally with the greatest distance between setae 1; setae equally spaced, 1 and 2 slightly longer than 3, setae 1 either level with the end of the premental sclerite or posterior to it.
Thorax and abdomen: Body curved, head free, hypognathous. Dorsal and sternal plates of the prothorax relatively distinct. Spiracles with two annulated air tubes equal to or slightly longer than the width of the peritreme. Prothoracic spiracle larger than the abdominal ones, air tubes vertical, abdominal spiracles equal in size, air tubes postero-lateral. Setae relatively distinct, distribution as in plate XIV, agrees with the standard in all respects. - 109 -
Po1ygraphus rufipennis
This is the only species of this genus reported as occurring in Canada. Host trees are given as pine, spruce and larch althougn spruce is probably the favoured host tree. The following description covers the main features of the larva.
Head capsule: fig.27. Head free, as broad as long, widest at the centre, sides curved, posterior margin narrowly rounded. Dark amber in colour, slightly less so in the mid-dorsal region, darker on the anterior of the frons and around the oral foramen. Frons triangular, almost one-half the length of the head capsule. Coronal and frontal sutures distinct. Endocarinal line distinct. Antenna a central cone in a basal, membranous area with several, short, basal setae. Setal pattern as in fig. 27 and Table III. Dorsal epicranial setae 1 and 2 approximately level in position. Posterior epicranial setae minute. Ventral epicranial seta 1 and 2 conspicuous.
ClyPeus: fig. 64. Sides angulate, anterior margin slightly emarginate. Basal, pigmented band with a sinuate, anterior margin, approxima.tely one-third to one-half the depth of the clypeus, indented medially. Clypeal seta 1 approxi mately twice the length of 2.
Labrum: fig. 64. Sides sub-parallel, anterior margin protuberent medially. Tormae short, stout, curved with a convex, mesal side. Three pairs of dorsal setae.
One median and paired lateral sensilla. - 110 -
Epipharyngeal lining: fig. 7S. One pair of short, antero-median setae and three pairs of long, antero lateral setae on the anterior margin. Three pairs of median epipharyngeal setae, equally spaced with the two anterior pairs usually in front of the t.ormae, Paired clusters of three sensilla between the second and third pairs of setae.
Mandible: fig. 95. Three incisoral teeth, apical and sub-apical acute, third obtuse but not emarginate. The distal portion of the mandible bearing the teeth is smaller in width and thickness than the basal half thereby forming a sort of transverse ridge about the centre. Two setae below the ridge line, close together and beside each other. One sensillum on the mesal surface and two sensilla on the proximal margin of the dorsal surface.
Maxilla: fig. 43. Palpus two-segmented, segment one with a short seta and two sensilla, segment two with one sensillum and apical papillae. Stipital seta 1 in the proximal third of the stipes. Palpiferal setae on the sclerotized margin of the membranous area at the base of the palpus. Lacinial lobe with seven dorsal setae and a distal group of five .ventral setae and one ventral seta and sensillum at the base of the lobe.
Labium: fig. 43.
Posterior part of premental sclerite distinct, median, longitudinal strip more darkly pigmented, sides of the median anterior projection almost parallel. Palpus two-segmented, each segment with one sensillum on the ventral surface, the second segment with apical papillae. Two pairs of - 111 - setae and one pair of sensilla on the ligula. One pair of long, prelabial setae. Postlabial setae 1 to 3 arran~d in a triangular formation, the distance between setae 1 the least and between setae 2 the greatest; setae 2 closer to 3 than to 1; setae 1 on the same level as or posterior to t he end of the premental sclerite.
Thorax and abdomen: Body curved, head free, hypognathous. Dorsal and sternal plates of the prothorax relatively distinct. Spiracles with two annulated air tubes equal in length to the width of the peritreme; prothoracic spiracle larger than the ones on the abdomen, air tubes vertical; abdominal spiracles approximately equal in size, air tubes postero-lateral in position. Setae relatively distinct, distribution as in plate XIV, agrees with the standard.
Pityophthorus consimilis
" nudus " puberulus " pulchellus
The genus Pityophthorus is represented by ten recorded species in eastern Canada of which larvae of the four species listed above and two additional species, the adults of which could only be identified to genus, were available for examination. Larvae of the four species could not be separated on the basis of anatomical characters. The species are small, found mostly in smaller twigs and tips of pine and spruce trees. The following description has been prepared from an examination of the larvae of the four species listed above and the two ' unidentified spepies. - 112 -
Head capsule: Fig. 29 Head free, approximately as broad as long, widest at the centre, sides curved, posterior margin rounded, amber coloured, darker on the anterior of the frons and around the oral foramen. Some specimens with a less deeply pigmented strip beginning at the frontal suture and proceeding posteriorly, parallel to the coronal suture half the distance to the posterior margin. Frons triangular, posterior end slightly rounded. Coronal and frontal sutures distinct. Endocarinal line distinct, extending almost half the length of the frons, with a slight longitudinal depression over the endocarina. Antenna a central cone in a membranous, basal area with a number of basal setae of which three lateral ones are longer than the others, but shorter than the central cone. The distribution of setae as in fig. 29 and Table III. Setae relatively distinct with the exception of the minute posterior epicranial setae.
Clypeus: fig. 65.
Sides rounded to angular, anterior margin USllSlly deeply emarginate in the centre. Basal, pigmented area very narrow. Clypeal seta 1 and 2 subequal, 1 longer than 2.
Labrum: fig. 65. Sides sub-parallel, anterior margin slightly protuberent medially. Tormae long and slender, slightly divergent posteriorly. Three pairs of dorsal setae, one median and paired lateral sensilla.
Epipharyngeal lining: fig. 74. Three antero-median setae and three pairs of antero-lateral setae. Three pairs of median epipharyngeal setae, equally spaced with the most anterior - 113 -
pair immediately posterior to the three antero-median setae. A pair of sensilla between the second and third pairs of setae and posterior to the third pair of setae.
Mandible: fig. 102. Three incisoral teeth, all acute. Two setae on the dorsal surface in vertical alignment. One sensillum on the mesal surface and two sen8il18 on the proximal margin of the dorsal surface.
Maxilla: fig. 52. Palpus two-segmented, segment one with a long seta and two s ensilla, segment two with one sensillum and apical papillae. In some specimens, an accessory process present, equal in length to the distal segment of the palpus, on the outer, distal margin of the first segment of the palpus. Stipital seta 1 immediately posterior to the midline of the stipes. Palpiferal setae in the membranous area at the base of the pal.pua, Lacinial lobe with seven dorsal setae and a distal group of five ventral setae and one ventral seta and a sensillum at the base of t he free lobe.
Labium: fig. 52. Posterior part of premental sclerite triangular, slightly constricted. A median, longitudinal streak of darker pigment present. Palpus one segmented, paired sensilla located in position usually occupied by the basal segment of the palpus. Distal segment of the palpus with one sensillum and apical papillae. Two pairs of setae and a pair of sensilla on the ligula. One pair of long, pre18bial setae. Postlabial setae in a straight line arrangement proceeding antero-mesally with the distance - 114 - between setae 1 the greatest, setae equally spaced, 1 and 2 slightly longer than 3, setae 1 on a line with or anterior to the posterior of the premental sclerite.
Thorax and abdomen: Body curved, head free, hypognathous. Dorsal and sternal plates of the prothorax only lightly pigmented and indistinct. Spiracles with two annulated air tubes slightly longer than the width of the peritreme.
Prothoracic spiracle larger than abdominal ones, air tubes vertical.
First abdominal spiracle slightly larger than those on segments two to eight, air tubes postero-lateral in position. Distribution of setae as in plate XIV, agrees with the standard except for the occurrence of eleven or twelve dorsal prothoracic setae and three alar setae opposed to two in the standard.
Scolytus piceae
2. piceae is the only species in this genus reported as occurring in conifers in eastern Canada. It OCCurSffiOst commonly in spruce although reported from balsam fir as well. The specimens examined in t his study were all collected from the small branches of dying spruce trees and spruce logging slash. Most of the engravings score the wood deeply. The following description covers the main features of the larva.
Head capsule: fig. 19.
Head retracted, longer than wide, sides sub-parallel, posterior margin rounded. Pigmentation mostly absent except for the anterior region of the frons and around the oral foramen. Frons triangular, broader than - 115 - long, posterior end a cute angled. Coronal and frontal sutures indistinct. Errlocarinal line indistinct. Antenna a central cone in a basal, membranous area with several basal setae, one of which, mesad of the cone, is longer than the cone. Setae are all small and indistinct, distribution as in figure 19 and Table III. Six pairs of setae on the frons in place of the usual five pairs on the frons of most scolytid larvae studied. All epicranial setae smaller than frontal setae and located immediately posterior and lateral to the frons.
Clypeus: fig. 62. Sides sub-parallel, anterior margin broadly emarginate. Basal, pigmented band very narrow. Clypeal setae 1 and 2 sub-equal, 1 longer than 2.
Labrum: fig. 62. Sides rounded, anterior margin broadly rounded, slightly protuberent in the centre. Tormae long, slender, diverging posteriorly. Posterior half of the labrum is more darkly pf.gmented than the anterior half. Three pairs of dorsal setae. One median and paired lateral sensilla.
Epipharyngeal lining: fig. 70. Two median and three pairs of antero-lateral setae on the anterior margin. Four pairs of median epfphar'yngeal, setae, two pairs located immediately posterior to the antero-rnedian setae and two pairs located more posteriorly, between the tormae. One pair of sensilla between the posterior pairs of setae. lwlandible: fig. 93. Two teeth, apical and sub-apical roundly acute. When the mandibles have been used for some time, the end is chisel-shaped, nearly all evidence of - 116 - the original dentation lacking. Two setae on the dorsal surface close together and beside each other. One sensillum on the mesal surface and two on the proximal margin of the dorsal surface.
Maxilla: fig. 46. Palpus two-segmented, the basal segment with a long seta and two s ensilla and the distal segment with one sensillum and apical papillae. Stipital seta 1 located centrally in stipes in a small, non-pigmented area occupying approximately one-third the length of the atd.pes , The stipital sensillum posterior to the non-pigmented area. Palpiferal setae on the border of the membranous area at the base of the pal.pue, Lacinial lobe with seven, short, dorsal setae and a distal group of five, ventral setae and one ventral seta and sensillum at the base of the free lobe.
Labium: fig. 45. Posterior end of the premental sclerite distinct fram the body of the sclerite, sides of sclerite parallel. Palpus two-segmented, basal segment with two sensilla and distal segment with one sensillum and apical papillae. Two pairs of setae and one pair of sensilla on the ligula.
A pair of long prelabial setae. Postlabial setae in a straight line arrangement proceeding antero-laterally with t he least distance between setae 1; setae equally spaced, setae 1 posterior to the premental sclerite.
Thorax and abdomen:
Head retracted, slightly prognathous, thoracic region enlarged. Dorsal and sternal plates of the prothorax light~ pigmented and indistinct.
Spiracles circular, prothoracic spiracle larger than the abdominal ones - 117 -
which are equal in size. Setae are all small and inconspicuous, distribution as in plate XIV, agrees with the standard.
Trypodendron bivittatum
I. bivittatum is one of the two species of ambrqsia beetles studied. A knowledge of the source of material being examined and the habitat of the larvae will be of value here since there are only a few species of ambrosia beetles found in eastern Canada compared to true bark beetles. The following description covers the ffiainfeatures of the larva.
Head Capsule: fig. 18.
Head partially retracted, slightly longer than wide, sides curved, posterior margin broadly rounded. Pigmentation lacking except for the anterior part of the frons and a round the oral foramen. Frons triangular, posterior end acute angled. Coronal and frontal sutures indistinct.
Endocarinal line indistinct, extending one-half the length of the frons. Antenna a central cone in a basal, membranous area with a number of basal setae, two of which approximately one-third the length of the cone. All setae minute and inconspicuous. Dorsal epicranial setae 1 and 2 very minute possibly due to the retraction of the head into the prothorax. Frontal seta I very minute. Ventral epicranial setae 1 and 2 relatively large. Distribution of setae as in figure 18 and Table III.
Clypeus: fig. 68.
Sides angulate, anterior margin broad~ emarginate. Basal pi~ented band narrow following the contour of the fronto-clypeal suture. Clypeal seta 1 slightly longer than 2. - 118 -
Labrum: fig. 68. Sides parallel, anterior margin protuberent medially. Tomae long, slender, approaching and fusing posteriorly. Three pairs of slender, dorsal setae. One median and paired lateral sensi11a.
;§pipharyngeal lining: fig. 80. One pair of antero-median setae and a single pair of antero-1ateral setae on the anterior margin. No median epipharyngeal setae on the specimens examined.
Mandible: fig. 97. Three incisoral teeth, apical and sub-apical acute, third obtuse acute. TWo setae on the dorsal surface, not close together, on approximately the same level. One sensillum on the mesal surface and two on the proximal margin of the dorsal surface.
Maxilla: fig. 54. Palpus two-segmented, segment one with a short seta and two sensilla, two with one sensil1um and apical papillae. Stipital seta 1 in the distal half of the et.Lpea, Outer palpiferal seta on the sclerotized margin of the membranous area at the base of the palpus and the inner seta in the membranous area. Lacinial lobe with seven dorsal, slender and pointed setae, a distal group of five ventral setae and one ventral seta and a sensillum at the base of the lacinial lobe.
Labium: fig. 54. Premental sc1erite broadly rectangular with a median and two lateral anterior projections. Palpus two-segmented, each segment with one sensi1lum on the ventral surface, the distal segment with apical papillae. - 119 -
Two pairs of setae and a pair of sensilla on the ligula. One pair of long prelabial setae. Usually only three pairs of postlabial setae; setae 1 lateral to the posterior margin of the premental sclerite, setae 2 and 3 lateral to the anterior part of the premental sclerite, distance between setae 2 the greatest; setae 2 much closer to 3 than to 1. In some specimens examined, a supernumerary seta was present lateral to seta 1 (indicated by dotted lines, fig. 54). lhorax and abdomen: Body curved, head slightly retracted into the prothorax, prothorax slightly enlarged. Dorsal and sternal plates of the prothorax only slightly pigmented, indistinct. Spiracles small, inconspicuous, circular, the prothoracic spiracle larger than the abdominal ones, the first abdominal spiracle slightly larger than those 'on segments two to eight. Setae very minute and inconspicuous, distribution being as in plate XIV. Considerable departure from the standard. Eleven or twelve setae on the dorsum of the prothorax in place of eleven; three setae in place of one on dorsal fold I of the second and third thoracic segments; four setae in place of 2 on the alar areas of the same segments and two mediosternal setae in place of one on these segments; dorsal folds I and III of abdominal segments one to eight have two and four setae in place of one and five respectively; on the same segments, one seta on the ventropleural lobe in place of two, one mediosternal seta in place of two and three laterosternal setae in place of one on the standard; the ninth abdominal segment with only three dorsal setae in place of five on the standard. - 120 -
VIII. OBSERVED AND RECORDED HOSTS
Certain species of bark beetles are host specific to one or more species or to a particular genus of trees. A knowledge of these host specificities becomes very useful in the identification of both adul.ts and larvae if the .sou rce of the specimens being examined is known. To supplement the information given in the key in section VII, the following list of hosts which may be found in eastern Canada has been prepared from records published by Swaine (1918), Blackman (1928) and Chamberlin (1939). The list of hosts given by these authors has been augmented in certain cases qy records of collections made by the writer.
Species of bark beetle Hosts
Crypturgus atomus Various species of pine and spruce; balsam fir, eastern larch
Dendroctonus piceaperda White, black and red spruce.
" rufipennis White and jack pine
II simplex Eastern larch
" valens White and red pine. tlylurgops pinifex Various species of eastern pines,
spruce and rarely in eastern larch.
Ph10eosinus canadensis Eastern white cedar. - 121 -
Polygraphus rufipennis White, black and red spruce, eastern larch, rarely in balsam fir.
Scolytus piceae White, black and red spruce, eastern larch and balsam fir.
Conophthorus coniperda Cones of white pine.
" resinosae Cones of red pine.
Dryocoetes affaber White, red and jack pine, balsam fir.
r have found it in eastern larch
and white and black spruce.
" americanus White and red spruce, white pine. r have found it in red pine and .bl ack
spruce.
Gnathotrichus materiarius. All species of pine, spruce and eastern larch, eastern hemlock and
balsam fir.
1.£2. borealis White and red spruce, doubtfully from balsam fir and eastern hemlock.
" calligraphus White pine.
" chagnoni White and red spruce, white pine. r have found it in jack pine.
" perturbatuB White spruce. r have found it in black spruce. - 122 -
White and red pine, white spruce, I have found it in jack pine and black spruce.
Qrthotomicus caelatus White pine, eastern larch, species
of spruce. I have found it in
red pine.
Pityogenes hopkinsi White, red and jack pine, white spruce.
II plagiatus Red and jack pine.
Pityokteines sparsus Balsam fir fityophthoruB consimilis White, red and jack pine, red
spruce, balsam fir. I have found it in white and tiBck spruce.
II nudus Various species of pine and spruce.
II puberulus White, red, jack and Austrian pine, red spruce and balsam fir.
" pulchelluB Red spruce, balsam fir, jack pine.
II sp. lIall White spruce by the writer. " sp, lib" Jack pine by the writer.
Trypodendron bivittatum White, red and jack pine, white
red and black spruce, balsam fir,
eastern hemlock. - 123 -
IX. AVERAGE LENG'IH OF LARVAE AND ADULTS OF SPECIES EXAMINED
In certain cases, the task of determining species of bark
beetles from larval characteristics may be facilitated if the
approximate size of mature larvae of different species is known as
well as the average size of corresponding adults. Obviously, if a
mature larva with a length of 2.5 mm, has been keyed out to a species
which has an adult length of approximately 5.0 mm, , an error in
interpretation of certain characters has been made somewhere in the
larval key. To provide such' assistance, measurements of a number of
mature larvae of the species in this study were made by means of an
ocular micrometer on a binocular microscope. The results converted to
millimetres of length have been detailed below with the number of
specimens examined in order to indicate the probable reliability of
the figures. In certain cases it will be noted that only two specimens
were available and consequently not too much weight can be given to
the average length obtained. Where the normal shape of the larva was
curved with the dorsal surface convex, no attempt was made to
straighten it. The measured length in such cases was an arc through
the curvature of the body from the most anterior part of the head to
the most posterior part of the body, usually the dorsal surface of the
ninth segment. In a larva which was nonnally straight, the measured
length was from the most anterior to the most posterior parts of the
body. To supplement the larval measurements, the average lengths of
corresponding adults, as recorded by Swaine (1918) and Chamberlin (1939),
have been entered in the last column of the table. Certain of the
measurements are not very precise but they will serve as a guide in decisions as to the suitability of a determination. - 124 -
Species Larvae Adults Mean length Length in in nm, Frequency mm,
CryPturgus atomus 19 1
~endroctonus piceaperda 23 6.75-6.2 " rufipennis 6 6 fI simplex 9 3.5 -5.2 " valens 10.1 10 5.0 -9.0 Hylurgops pinifex 19
Phloeosinus canadensis 20 Polygraphus rufipennis 20 Scolytus piceae 5
Conophthorus coniperda 7 " resinosae 12 2.75-3.25 DEYocoetes affaber 8 2.75 " americanus 16 3 -4 Gnathotrichus materiarius 11
~ borealis 2 3.25-4.0 " calligraphus 5 " chagnoni 2 " perturbatus 13 " 15 Orthotomicus caelatu5 12
Pityogenes hopkinsi 13 2
fI plagiatus 10 2 fityokteines sparsus 13
Pityophthorus consimilis 1.9 14 " nudus 10 - 125 -
Pityophthorus puberulus 2.4 2 1.3 -1.6 " pulchellus 2.3 2 1.6 " "a" 1.6 9 " libII 2.8 20 Trypodendron bivittattUn 3.5 10 3
X. SUMMARY
A preliminary study has been made of the use of the external anatomy of the larvae of bark beetles for identification of genera and species of the family Scolytidae. Owing to scarcity of material, a fact which, in itself, indicated the lack of knowledge on this aspect of such an important group of insects, the study was confined to larvae of some of the species breeding in coniferous trees in eastern Canada.
As more material becomes available, the scope of this investigation will be broadened.
The external anatomy of the larvae of thirty of the forty species of bark beetles recorded as occurring in coniferous trees in eastern Canada was studied. These thirty species represented fifteen of the nineteen genera found in this limited territory.
A key, based on larval characteristics, has been prepared with which it is possible to determine to the genus the thirty species.
Fortunately, of the fifteen genera available for study, seven are represented by one species only in eastern Canada so t he generic key - 126 -
in these instances is in reality a specific key. Another genus, while
it has more than one species in it occurring in eastern Canada, has
one only attacking coniferous trees, therefore, in this instance also,
the generic key is a specific key. Of the remaining genera, it was
only possible to separate the larvae of the four species of the genus
Dendroctonus on the basis of larval characters, and a key has been
prepared to do this. In one other genus, ~ it was possible to separate one species, I. pini, from the larvae of four other species availaoe for study.
One hundred and five drawings illustrating the chief
characteristics and variations found in the larvae examined have been
prepared to supplement the information given in the keys and text.
While larval identification alone might prove impractical
in certain cases, when taken together with other information already
available such as keys based on adult characteristics, host specificity
shown by many species and characteristic gallery construction, it is
believed that a useful contribution has been made to t he tools at hand
. for taxonomic work in this group of insects. - 127 -
XI. BIBLIOGRAPHY
Anderson, W.H.
1941. The larva and pupa of Cylindrocopturus furnissi Buchanan (Coleoptera, Curculionidae). Froe. Ent. Soc. Wash. 43:152-155.
1947. A terminology for the anatomical characters useful in the taxonomy of weevil larvae. Proc , Ent, Soc. Wash.49(5) :123-132.
1948&. A key to the larvae of some species of Hypera Germar, 1817 (. Phytonomus Schoenherr, 1823) (Coleoptera, Curculionidae) Proc. Ent. Soc. Wash. 50(2):25-34.
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Wallace, P.P. and R.L. Beard 1942. Larval characteristics of certain elm bark infesting Coleoptera. Can. Ent. 74(5):86-87. PLATES I to XIV Figure 1. Dorsal aspect of larva of Hylurgops pinifex " 2. Lateral rt " II II " " 3. Ventral " II II II II ••
Als - Setae of abdominal segment, fold I AllIs - II II II " If III lTs - Prothoracic dorsal setae 2TIs - Dorsal setae of mesothorax, fold I 2Tlls _ If "" " " II 3TIs II " " metathorax, It I 3TIIs - If If " " " II 9As - Setae on dorsum of 9th abdominal segment lOAs "" If "10th" II Lsts - Laterosternal setae Msts - MSdiosternal setae Peds - Setae of pedal lobes of thorax Ps - Pleural setae Sps - Spiracular setae Sts - Sternal setae Vpls - Ventropleural setae DPI. Dorsa l Plat e / Do.....'Plate \ / \ / , .Mu . VPI • / -, -, - - - VPI. ------= PROTHORAX - t..f";ti:: __ VP I. _ ~ 2TJIs ~ ~_L.~ ~'_~~ lotESOTHORAX_
...eoOMEN METATHORAX Peds - - - ...IlDOMEN DPI. I . , - S pa ---.w.b------"'Is 2 2 Jins---",- - --t----)-/ l.ta -- ·...Is -'VPI. - -- ·; 3 w - - -- I\) ~/ -- --- 4 - - - .. ~~ ::-- - -3 "'1Is ------:-:::4 5 ~~' S r-- ;>\ 1------__ ------6 VCntr~1cIra1 ,- 6 , ~ 7 Pleural 'ro ..... 7
II ------' , 10 , .. ------
',:'! \ ' .... ,....II .... " ... , " PLATE II Figure 4. Posterior aspect of segments 9 and 10 of Hylurgops pinitex
It 5. Anterior aspect ot head capsuJe of fi. pinitex
It It 6. Dorsal It It If If li. pinitex " 7. Ventral If u " " " fi. pinitex It a. Dorsal aspect of Labrum and Clypeus of li. pinifex
9As - Setae of 9th abdominal segment 10As II tllOth If " Ams - Antero-median setae Clps - Clypeal setae Clpsl - Clypeal sensilla dam - Dorsal articulatory process of mandible Des - Dorsal epicranial setae Desl It It sensilla Fa - Frontal setae Fsl It sensilla Ha - Hypostomal apodeme Hs "suture Les - Lateral epicranial setae Lesl - tl It seneilla Lms - Labral setae Lmsl - It sensilla Pes - Posterior epicranial setae Pesl _ It . If sensilla Poc - Postocciput Pos - Postoccipital suture Pe - Pleural setae Sts - Sternal setae tb - tentorial bridge Ves - Ventral epicranial setae Vesl -" "sensilla 9AS
Frantal ~hdian , Frontogono' suture /tubcrcl~ suture
SUbgonal _ inflccUon
. -Hypostomal I apodcmc Maxillary / \ I \ articulation \ TG\torial Hypopharyngoal • - --- ·Sts Anus/ " bridgo bra con 4 5 / Median tubuclc
...dam
Lu2' suture I,
-. Frontal suture - -Endocarinal 11M
- -Coronal suture
Pos _ w _
. _:- -~- Ecdysial SUlcus 6 /Hypopharyng ~Antcrior Los 2' tentorial Qrm I' I, ·-Hs Labrum- --Ha Vul- -Maxillary articulation ClypoUS -- Pigmontod area apodcmc 7 8 PLATE III Figure 9. Ventral aspect of labium and maxillae of Hylurgops pinifex II 10. Dorsal aspect of maxilla of Hylurgops pinifex II 11. Ventral aspect of left mandible of tl. pinifex n 12. Dorsal aspect of left mandible of !!. pinifex II 13. Abdominal spiracle of !!. pinifex .. 14. Abdominal spiracle of Phloeosinus canadensis II 15. Lateral aspect of hypopharynx of tl. pinifex II 16. Epipharyngeal lining of !i.. pinifex Als • Antero-lateral setae Ams II -median setae DLcs - Dorsal lacinial setae Esl - Epipharyngeal sensilla Lis - Ligular setae Lisl - Ligular sensilla Mds - Mandibular setae Masl - II sensilla Mes - Median epipharyngeal setae Mxps - Seta on maxillary palpus Plbs - Postlabial setae PIs - Palpiferal setae Plsl - .. sensilla Pmtsl - Premental sensilla Prbs - Prelabial setae Sts - Stipital seta Stsl - II sensilla VLC8 - Ventral lacinial setae VLeal _.. .. sensilla Mxpsl - Sensilla on maxillary palpus VLc. Latlnlal lobe Mxp.\· \ /':11\ ,Papillae , ' , / Paotlablum /. /".. /. /. /. Prcmcntum 10 9 ::: -=---~,fTccth Teethe::::':" / / ( Air tubes I' ( \ A ( 1\ 1 \ ( 1 , ( I' ( 1 ( I _Md.1 - Dorsal articulatory _Ventral eJ articulatory groove 13 condyle -Adductor - Adductor Abductor tendon tendon tendon @ 14 11 12 ,Ams ~' --:'\ I'. I ,~\~,: 'OlSophagu. .heath -Torma. / Epi.tomal apademe 15 16 PLATE IV Dorsal aspect of head capsule of : Figure 17. Phloeosinus canadensis II 18. Trxpodendron bivittatwn " 19. Scol:vtus piceae II 20. Orthotomicus caelatus " 21. Ips pini II 22. II perturbatus I O.2mm I 17 " ,Antenna I Mta 18 \ . i ' , .... \' ~ "- j , -{~ ."' ..,', I . ,'...... ~ ,02mm I 19 20 Tubcrclu :\ I 0 2 mm I I Qam", I 21 22 PLATE V Dorsal aspect of head capsule of: Figure 23. Dendroctonus piceaperda II 24. Pityokteines sparsus II 25. Pityogenes hopkinsi It 26. Dryocoetes affaber " 27. Polygraphus rufipennis " 28. Crypturgus atomus I 0 .2",m I I 02mm I I Q2mm I O.2mm 25 26 I Q2mm I I aim", I 27 28 PLA'lE VI Dorsal aspect of head capsule of: Figm-e 29. Pityophthorus consimilis " 30. Conophthorus resinosae " 31. Gnathotrichus materiarius Part of a segment showing the arrangement of the spiracle in: Figure 32. Dendroctonus valens II 33. " rufipennis II 34. " piceaperda 35. simplex Des - Dorsal epicranial setae Fs - Frontal setae Les - Lateral epicranial setae Lesl - Lateral epicranial sensilla Pes - Posterior epicranial setae Ves - Ventral epicranial setae 0.2mm 30 - -PIgmented lu berc I. Spiracle- ~----= --PIgmented dorlOillcurol Iobc ,I , - '. .02mm No~lgm.nl.d ar.a I 02mm 31 32 . Diler,tc ....p.rlli•• I _.Plgmented- _ _ tUbercle -- Spiracle -- Splracl. -- 1'lllm. nted Neiii'·P111m.nt.d dorsa_pleural dorsa-pleural lobc lobc 10.2mm I 0 2"'''' 33 34 , I 35 , 0 2"'''' I PLATE VII Figure 36. Dorsal plates on segments 7, 8 and 9 of Dendroctonus rufipennis II 37. Dorsal plates on segments 7, 8 and 9 of Dendroctmus piceaperda II 38. Dorsal plates on segments 8 and 9 of Dendroctonus va1ens II 39. Anterior aspect of left hal! of the head capsule of a weevil larva, Pissodes sp. II 40. Lateral aspect of the folds in an abdominal segment of a weevil larva, Pis80des sp, Fs - Frontal suture Dorsal pial. trac. Sq",.nl DarlO. l pial. lrace ." • : . ~ 0• • ~ . " ... : ..... ' . ' . ' Dorsal platt '.' ' " ' . . 0 ·2mm , 36 ().2mm I I :ri~;": ' :'; ,~li;:':" J " . ', '. :;"FoI4' .. ..'?}f-.... ~:Y"- . ' .: ;/ / ". '. -( : ; '. .: /. .. .:- / ---- Any, 38 ,oa "'''' , 40 -St>lraclc ,oallllll , PLATE VIII, Ventral aspect of labium and maxillae of: Figure 41. Dendroctonus piceaperda " 42. Cmturgus atomus n 43. Polygraphus rufipennis " 44. Phloeosinus canadensis It 45. . Scolytus piceae " 46. Pityogenes hopkinsi I Olmm • 41 I CHmm 42 Olmm I 44 ,Olmm I 43 ~CCCllOry " ,roecu ,~Imrft 45 46 ,~~~ , PLA'lE IX Ventral aspect of labium and maxillae of: Figure 47. Orthotomicus caelatus It 48. Pityokteines sparsus It 49. Ips pini If 50. Dryocoetes ame ricanus " 51. Conophthorus resinosae " 52. Pityophthorus consimilis It 53. Gnathotrichus materiarius It 54. Trypodendron bivittatum I Q.lmm I 49 50 , 0 1111111 0.1 mm 51 52 I 0.1111111 54 I 01111111 I PLATE X Dorsal aspect of clypeuB and labrum of: Figure 55. Dendroctonus rufipennis II 56. Cr,ypturgus atomus II 57. Pityokteines sparsus II 58. Ips perturbatus II 59. Orthotomicus caelatus " I:IJ. Pityogenes hopkinsi II 61. Phloeosinus canadensis II 62. Scolrtus piceae " 63. Dryocoetes americanus II 64. Polygraphus rufipennis II 65. PitYophthorus pulchellus II 66. Conophthoru8 coniperda II 67. GnathotrichuB materiariu5 " 68. Tr,ypodendron bivittatum O.lmm I o.oamm, 55 56 57 QOllmm O.oemm 61 Q.Qllmm 63. QOllmm 'Pigmented band 65 t-----="--o.lmm _ QQllmm 67 Q.Qllmm 68 Q.Qllmm PLATE XI Epipharyngeal lining of labrum and c1ypeus of: Figure 69. Cmturgus atomus II 70. Scolytu8 piceae II 71. Phloeosinus canadensis If 72. Orthotomicus cae1atu8 II 73. Conophthorus coniperda II 74. Pityophthorus pulche1lu8 II 75. Pityogenes hopkinsi " 76. Pityokteines sparsus tI 77. Dryocoetes americanus " 78. Polygraphus rufipennis II 79. Gnathotrichus materiariuB .. 80. Trypodendron bivittatum Als - Antero-1ateral setae Ams - Antero-median setae Mes - Median epipharyngea1 setae :";J f , ' \2l~ :1 , (1 -/" II I I I i: ~ ~ . i '~ ' ',J ,0.02mm Pigmented I" · ,,' 008mm {II band 69 70 71 I o .oemm O lmm o.oemm O.OSmm 72 73 74 ooemm 0 .08mm Q,oemm 75 76 77 Ami O lmm o.oemm 0.08mm 78 79 80 Epipharyngeal lining of labrum and clypeus of: Figure 81. Ips pini II 82. II calligraphu8' r II 83. " perturbatus It 84. It borealis " 85. It chagnoni II 86. Dendroctonus simplex " 87. " piceaperda " 88. " rufipennis II 89. II valens " 90.Sclerotized plates on pronotum of Dendroctonus valens Als - Antero-lateral setae Ams - Antero-median setae Mes - Median epipharyngeal setae ~Ill' (.: ,I'"I, ,", , o.Imm ().Imm 81 82 83 ().Imm ().Imm ().Imm 84 85 86 ()'2mm Q.lmm ().Imm 87 88 89 Dorlell plal.. ;' ~ , ... ,- - - 90 ().4mm PLATE XIII Dorsal aspect of right mandible of: Figure 91. Ips pini " 92. Pityogenes hopkinsi II 93. Sco1ytus piceae II 94. Crypturgus atomus II 95. Po1ygraphus rufipennis II 96. Dryocoetes americanus " 97. Trypodendron bivittatum II 98. Pityokteines sparsus \I 99. Ph1oeosinus canadensis " 100. Gnathotrichus materiarius \I 101. Conophthorus resinosae II 102. Pityophthorus pulchellus " 103. Dendroctonus rufipennis \I 104. OrthotomicUB caelatus \I 105. Hy1urgops pinifex Q.2rnm I 91 93 I 02mm I 94 I 005mm I 97 I Q.lmm Olmm 100 O lmm I · 10~, 103 I O.2mm I ·Q.-I mm I 105, O.2mm I PLATE XIV Chart showing the distribution ot setae on the thorax and abdomen ot representatives ot the 15 genera studied Note: A blank square indicates that the number of setae present agrees with the model number given in the left-hand column...... 0" ~ ...... !. '-" ~ ~ ~ .:e. DISTRIBUTION (/) III III III " CIl ::J ::J ... ::J 411 0 III III '- 8 .J:: CIl E ::J ::J e III .!:! CIl 0 '- 0 III .J:: 0 .!:! OF ci ::J .J:: s .s" .J:: e ~ ... Q. s CIl ...... " ...'- e' 0 CIl ft ::J .J:: 0 ...s l s .J:: 0 ::J 8 0 '- ... Q. en .Jc Q. " ... '- :?' en :... u" 0 0 0 0 0 .J:: - Q. :... 0 0 .J:: Q. ... SETAE ~ " :... :... :... " 0 0" :... c: .E -0 c: :... III ...... :... c: " '- " :... .J:: -0 U 0 '- '- ... ~ U 0" .:r Q. Q. (/) U 0 ~ 0 if Q.'- if I- C) PROTHORAX Dorsal II 11-12 1M2 12 V~ntropl~ural lobe 2 Mediostunal I Lctercste rna! 3 4 4 Pedal lobe 2 3-4 3-4 4 MESO-& METATHORAX Dorsal fold I I 3 ~ .. .. II 5 Alar area 2 3 3 3 3 ~ 4 Dorsopleural lobe I Ventropl~ural lobe I 2 Medlosternal I 2 2 LaterosternaI 3 4 4 Pedal lobe 2 3-4 3-4 4 3 SEGMENT 1-8 ABDOMINAL 1-7 • Dorsal fold I I 2 2: .. .. III 5 ~ 4:2 I Spiracular 2 I Dorsopleural lobe 2 I H , Ventropleural 2 I I I Med iosterna.1 2 I 3: I La terosternaI I 2 3 I 9th ABDOMINAL Dorsal 5 6· 6 4 3 3 Pleural 2 Sternal 2 10th ABDOMINAL Anal 2 " D. rufipennts has 8